2010 AMC 10B 考试题目

Scroll down and press Start to try the exam! Or, go to the printable PDF, answer key, or professional solutions curated by LIVE, by Po-Shen Loh.

All of the real AMC 8 and AMC 10 problems in our complete solution collection are used with official permission of the Mathematical Association of America (MAA).

Want to learn professionally through interactive video classes?

Learn LIVE

考试时间还剩下:

1:15:00

1.

What is 100(1003)(1001003)?100(100-3)-(100 \cdot 100-3)?

20,000-20,000

10,000-10,000

297-297

6-6

00

Answer: C
Solution:

We have that 100(1003)=10097=9700 \begin{align*}100(100 - 3) &= 100 \cdot 97 \\&= 9700\end{align*} and 1001003=100003=9997. \begin{align*}100 \cdot 100 - 3 &= 10000 - 3\\ &= 9997.\end{align*}

As such, their difference is: 97009997=297. 9700 - 9997 = - 297.

Thus, C is the correct answer.

2.

Makarla attended two meetings during her 99-hour work day. The first meeting took 4545 minutes and the second meeting took twice as long. What percent of her work day was spent attending meetings?

1515

2020

2525

3030

3535

Answer: C
Solution:

Note that 4545 minutes is 4560=34 \dfrac{45}{60} = \dfrac{3}{4} hours. The second meeting is then 234=32 2 \cdot \dfrac{3}{4} = \dfrac{3}{2} hours. Both meetings take a total of 34+32=94 \dfrac{3}{4} + \dfrac{3}{2} = \dfrac{9}{4} hours then. The percent of Makarla's work day spent attending meetings is 100%949=100%14=25%. 100 \% \cdot \dfrac{\frac{9}{4}}{9} = 100 \% \cdot \dfrac{1}{4} = 25 \%.

Thus, C is the correct answer.

3.

A drawer contains red, green, blue, and white socks with at least 11 of each color. What is the minimum number of socks that must be pulled from the drawer to guarantee a matching pair?

33

44

55

88

99

Answer: C
Solution:

To maximize the number of socks, we want to grab as many single socks as possible before getting a pair.

There are 44 colors, which means that we can draw one sock of each color before drawing a pair.

This means that it takes at least 4+1=54 + 1 = 5 socks to be draw before a pair is guaranteed.

Thus, C is the correct answer.

4.

For a real number x,x, define (x)\heartsuit(x) to be the average of xx and x2.x^2. What is (1)+(2)+(3)?\heartsuit(1)+\heartsuit(2)+\heartsuit(3)?

33

66

1010

1212

2020

Answer: C
Solution:

We have (1)=1+122=1, \heartsuit(1) = \dfrac{1 + 1^2}{2} = 1, (2)=2+222=3, \heartsuit(2) = \dfrac{2 + 2^2}{2} = 3, and (3)=3+322=6. \heartsuit(3) = \dfrac{3 + 3^2}{2} = 6.

Then 1+3+6=10. 1 + 3 + 6 = 10.

Thus, C is the correct answer.

5.

A month with 3131 days has the same number of Mondays and Wednesdays. How many of the seven days of the week could be the first day of this month?

22

33

44

55

66

Answer: B
Solution:

Note that 3131 days leaves a remainder of 33 when divided by 7.7.

This means that if the month starts on a Saturday, Sunday, Tuesday, or Wednesday, there will be an uneven number of Mondays and Wednesdays.

Then the month can only start on a Monday, Thursday, or Friday.

Thus, B is the correct answer.

6.

A circle is centered at O,O, AB\overline{AB} is a diameter and CC is a point on the circle with COB=50.\angle COB = 50^\circ. What is the degree measure of CAB?\angle CAB?

2020

2525

4545

5050

6565

Answer: B
Solution:

Consider the following diagram:

We have that AOC=18050=130. \angle AOC = 180^{\circ} - 50^{\circ} = 130^{\circ}.

Since AOC\triangle AOC is isosceles, we have that CAO=1801302=25. \angle CAO = \dfrac{180^{\circ} - 130^{\circ}}{2} = 25^{\circ}.

Since CAB=CAO,\angle CAB = \angle CAO, we have that CAB=25.\angle CAB = 25^{\circ}.

Thus, B is the correct answer.

7.

A triangle has side lengths 10,10, 10,10, and 12.12. A rectangle has width 44 and area equal to the area of the triangle. What is the perimeter of this rectangle?

1616

2424

2828

3232

3636

Answer: D
Solution:

To find the area of the triangle, we can drop the altitude to the side of length 12.12.

Then we have a right triangle with one leg 12÷2=612 \div 2 = 6 and hypotenuse 10.10.

The other leg has length 10262=64=8. \sqrt{10^2 - 6^2} = \sqrt{64} = 8.

The area of the triangle is then 8122=48. \dfrac{8 \cdot 12}{2} = 48.

The length of the rectangle is then 48÷4=12.48 \div 4 = 12. Its perimeter is 2(4+12)=216=32. 2(4 + 12) = 2 \cdot 16 = 32.

Thus, D is the correct answer.

8.

A ticket to a school play costs xx dollars, where xx is a whole number. A group of 99th graders buys tickets costing a total of \$\(48,\) and a group of \(10\)th graders buys tickets costing a total of \$\(64.\) How many values for \(x\) are possible?

11

22

33

44

55

Answer: E
Solution:

Note that xx must divide both 4848 and 64,64, which means that must divide their greatest common divisor.

The greatest common divisor of 4848 and 6464 is 16,16, which means xx divides 16.16.

1616 has 55 factors, namely all the powers of 22 up to 16.16.

Thus, E is the correct answer.

9.

Lucky Larry's teacher asked him to substitute numbers for a,a, b,b, c,c, d,d, and ee in the expression a(b(c(d+e)))a-(b-(c-(d+e))) and evaluate the result. Larry ignored the parentheses but added and subtracted correctly and obtained the correct result by coincidence. The number Larry substituted for a,a, b,b, c,c, and dd were 1,1, 2,2, 3,3, and 4,4, respectively. What number did Larry substitute for e?e?

5-5

3-3

00

33

55

Answer: D
Solution:

Ignoring the parentheses, Larry would get 1234+e=e8. 1 - 2 - 3 - 4 + e = e - 8.

Evaluating with the parentheses, one would get 1(2(3(4+e)))=1(2(1e))=1(3+e)=2e.\begin{align*} &1 - (2 -(3 - (4 + e)))\\ & = 1 - (2 - (-1 - e))\\ &= 1 - (3 + e) \\ &=-2 - e.\end{align*}

Both of these values are the same, so e8=2e e - 8 = -2 - e e=3. e = 3.

Thus, D is the correct answer.

10.

Shelby drives her scooter at a speed of 3030 miles per hour if it is not raining, and 2020 miles per hour if it is raining. Today she drove in the sun in the morning and in the rain in the evening, for a total of 1616 miles in 4040 minutes. How many minutes did she drive in the rain?

1818

2121

2424

2727

3030

Answer: C
Solution:

Note that 4040 minutes is 23\frac{2}{3} hours. Let Shelby drive hh hours in the sun.

Then she drives 23h\frac{2}{3} - h hours in the rain, which means she travels a total of 30h+20(23h)=10h+403 30h + 20\left(\dfrac{2}{3} - h\right) = 10h + \dfrac{40}{3} miles. We have this equals 16,16, so 10h+403=16 10h + \dfrac{40}{3} = 16 h=415. h = \dfrac{4}{15}.

Then Shelby drives 60(23415)=6025=24 60\left(\dfrac{2}{3} - \dfrac{4}{15}\right) = 60 \cdot \dfrac{2}{5} = 24 minutes in the rain.

Thus, C is the correct answer.

11.

A shopper plans to purchase an item that has a listed price greater than $ 100 and can use any one of the three coupons. Coupon A gives 15%15\% off the listed price, Coupon B gives $ 30 off the listed price, and Coupon C gives 25%25\% off the amount by which the listed price exceeds $ 100.

Let xx and yy be the smallest and largest prices, respectively, for which Coupon A saves at least as many dollars as Coupon B or C. What is yx?y - x?

5050

6060

7575

8080

100100

Answer: A
Solution:

Let pp be the price of the item. Then coupon A saves .15p..15p. Coupon B saves $ 30.

Coupon C will save .25(p100)=.25p25. .25(p - 100) = .25p - 25.

We must have that .15p>30 .15p \gt 30 p200 p \geq 200 and .15p>.25p25 .15p \gt .25p - 25 250p. 250 \geq p.

This shows that x=200x = 200 and y=250.y = 250. Therefore yx=50.y - x = 50.

Thus, A is the correct answer.

12.

At the beginning of the school year, 50%50\% of all students in Mr. Well's class answered "Yes" to the question "Do you love math", and 50%50\% answered "No." At the end of the school year, 70%70\% answered "Yes" and 30%30\% answered "No." Altogether, x%x\% of the students gave a different answer at the beginning and end of the school year. What is the difference between the maximum and the minimum possible values of x?x?

00

2020

4040

6060

8080

Answer: D
Solution:

To minimize x,x, we want to have as many kids as possible maintain their answer.

We then need at least 7050=2070 - 50 = 20 percent of the students to change their answer.

To maximize x,x, we can have everybody that answered no change their answer, but some who answered yes must stay yes.

We need 7050=2070 - 50 = 20 percent of the people who said yes to stay yes, which means only 5020=3050 - 20 = 30 percent can switch.

This makes the maximum percent of students that can switch 50+30=8050 + 30 = 80 percent. The difference is then 8020=60.80 - 20 = 60.

Thus, D is the correct answer.

13.

What is the sum of all the solutions of x=2x602x?x = |2x-|60-2x||?

3232

6060

9292

120120

124124

Answer: C
Solution:

We first take care of the outer absolute value. We have either x=2x602x x = 2x - |60 - 2x| or x=2x+602x. x = -2x + |60 - 2x|.

These simplify to x=602x and 3x=602x. x = |60 - 2x| \text{ and } 3x = |60 - 2x|.

We have 22 cases for each equation. For the first one, we have x=602x and x=2x60. x = 60 - 2x \text{ and } x = 2x - 60.

Solving both gives us 3x=60 3x = 60 x=20 x = 20 and x=60 -x = -60 x=60. x = 60.

For the other equation, we have 3x=602x and 3x=2x60. 3x = 60 - 2x \text{ and } 3x = 2x - 60.

Again solving both, we ahve 5x=60 5x = 60 x=12 x = 12 and x=60.x = -60. Note that xx cannot be negative since that means the original absolute value is negative, which is not possible.

Adding up all the solutions gives us 20+60+12=92. 20 + 60 + 12 = 92.

Thus, C is the correct answer.

14.

The average of the numbers 1,2,3,,98,99,1, 2, 3,\cdots, 98, 99, and xx is 100x.100x. What is x?x?

49101\dfrac{49}{101}

50101\dfrac{50}{101}

12\dfrac{1}{2}

51101\dfrac{51}{101}

5099\dfrac{50}{99}

Answer: B
Solution:

Recall that the sum of the first nn integers is n(n+1)2.\dfrac{n(n + 1)}{2}.

Then, we have that 991002+x100=100x, \dfrac{\frac{99 \cdot 100}{2} + x}{100} = 100x, which simplifies to 9950=(10021)x 99 \cdot 50 = (100^2 - 1)x=10199x, = 101 \cdot 99x, by difference of squares. Dividing gives us x=50101.x = \dfrac{50}{101}.

Thus, B is the correct answer.

15.

On a 5050-question multiple choice math contest, students receive 44 points for a correct answer, 00 points for an answer left blank, and 1-1 point for an incorrect answer. Jesse’s total score on the contest was 99.99. What is the maximum number of questions that Jesse could have answered correctly?

2525

2727

2929

3131

3333

Answer: C
Solution:

Let xx be the number of questions Jesse answered correctly and yy be the number he answered incorrectly.

Then 4xy=99 and x+y50. 4x - y = 99 \text{ and } x + y \leq 50.

We have that y=4x99 y = 4x - 99 5x9950. 5x - 99 \leq 50.

Rearranging and simplifying tells us that x29.8.x \leq 29.8. Since xx is an integer, its maximum value is 29.29.

Thus, C is the correct answer.

16.

A square of side length 11 and a circle of radius 33\dfrac{\sqrt{3}}{3} share the same center. What is the area inside the circle, but outside the square?

π31\dfrac{\pi}{3}-1

2π933\dfrac{2\pi}{9}-\dfrac{\sqrt{3}}{3}

π18\dfrac{\pi}{18}

14\dfrac{1}{4}

2π9\dfrac{2\pi}{9}

Answer: B
Solution:

Drop the altitude from OO to AB\overline{AB} at X.X.

Looking at the side lengths, we see that OBX\triangle OBX is a 30609030-60-90 triangle.

This means that the area of sector AOBAOB is 16π(33)2=π18. \dfrac{1}{6} \cdot \pi \cdot \left(\dfrac{\sqrt3}{3}\right)^2 = \dfrac{\pi}{18}.

We also have that the area of AOB\triangle AOB is 1223612=312.. \dfrac{1}{2} \cdot 2 \cdot \dfrac{\sqrt3}{6} \cdot \dfrac{1}{2} = \dfrac{\sqrt3}{12.}.

The area of the sector outside the square and inside the circle is then π18312. \dfrac{\pi}{18} - \dfrac{\sqrt3}{12}.

There are 44 of these regions, which gives us a total area of 4(π18312)=2π933. 4\left(\dfrac{\pi}{18} - \dfrac{\sqrt3}{12}\right) = \dfrac{2\pi}{9} - \dfrac{\sqrt3}{3}.

Thus, B is the correct answer.

17.

Every high school in the city of Euclid sent a team of 33 students to a math contest. Each participant in the contest received a different score. Andrea's score was the median among all students, and hers was the highest score on her team. Andrea's teammates Beth and Carla placed 37th37^\text{th} and 64th,64^\text{th}, respectively. How many schools are in the city?

2222

2323

2424

2525

2626

Answer: B
Solution:

Let there be xx schools. Then there are 3x3x participants in the contest.

Since everyone has a unique score, there is also a unique median. This means xx is odd.

Note there are at least 2323 teams, since otherwise a 64th64^\text{th} placed wouldn't exist.

We also have at most 2323 teams, since otherwise we have Andrea's place as being greater than Beth's.

This means that there are 2323 teams.

Thus, B is the correct answer.

18.

Positive integers a,a, b,b, and cc are randomly and independently selected with replacement from the set {1,2,3,,2010}.\{1, 2, 3,\dots, 2010\}.

What is the probability that abc+ab+aabc + ab + a is divisible by 3?3?

13\dfrac{1}{3}

2981\dfrac{29}{81}

3181\dfrac{31}{81}

1127\dfrac{11}{27}

1327\dfrac{13}{27}

Answer: E
Solution:

Note that abc+ab+a=a(bc+b+1). abc + ab + a = a(bc + b + 1). This means that if aa is divisible by 3,3, the whole expression is as well.

Since 20102010 is divisible by 3,3, we have that aa is divisible by 33 with probability 13.\frac{1}{3}.

Now consider aa not divisible by 3.3. For the expression to be divisible by 3,3, we must have that bc+b+1bc + b + 1 is divisible by 3.3.

This means that bc+b=b(c+1)2(mod3). bc + b = b(c + 1) \equiv 2 \pmod{3}.

The only possibility for this is that one of the factors is 22 mod 33 and the other is 11 mod 3.3.

For each of the two cases, there is a 13\frac{1}{3} chance that each of the factors is the desired modulus, for a probability of 1313=19.\dfrac{1}{3} \cdot \dfrac{1}{3} = \dfrac{1}{9}.

There are two cases, which means that this happens with a 29\dfrac{2}{9} probability.

The total probability is then 131+2329=1327. \dfrac{1}{3} \cdot 1 + \dfrac{2}{3} \cdot \dfrac{2}{9} = \dfrac{13}{27}.

Thus, E is the correct answer.

19.

A circle with center OO has area 156π.156\pi. Triangle ABCABC is equilateral, BC\overline{BC} is a chord on the circle, OA=43,OA = 4\sqrt{3}, and point OO is outside ABC.\triangle ABC. What is the side length of ABC?\triangle ABC?

232\sqrt{3}

66

434\sqrt{3}

1212

1818

Answer: B
Solution:

Consider the following diagram:

Using the formula for the area of a circle, we have that BO=156BO = \sqrt{156} since it is a radius.

Extend AO\overline{AO} to intersect BC\overline{BC} at X.X. Let ss be the side length of ABC.\triangle ABC.

Then we have that BX=s2 BX = \dfrac{s}{2} and AX=s32. AX = \dfrac{s\sqrt3}{2}.

We have that OXB\triangle OXB is right, which means that we can apply the Pythagorean Theorem. This gives us (156)2=(s2)2 (\sqrt{156})^2 = \left(\dfrac{s}{2}\right)^2+(s32+43)2. + \left(\dfrac{s\sqrt3}{2} + 4\sqrt3\right)^2.

Simplifying, we get 156=s2+12s+48 156 = s^2 + 12s + 48 s2+12s108=0 s^2 + 12s - 108 = 0 (s6)(s+18)=0. (s - 6)(s + 18) = 0.

Since ss is positive, we must have that s=6.s = 6.

Thus, B is the correct answer.

20.

Two circles lie outside regular hexagon ABCDEF.ABCDEF. The first is tangent to AB,\overline{AB}, and the second is tangent to DE.\overline{DE}. Both are tangent to lines BCBC and FA.FA. What is the ratio of the area of the second circle to that of the first circle?

1818

2727

3636

8181

108108

Answer: D
Solution:

Consider the following diagram:

We can see that the smaller circle is inscribed within an equilateral triangle of side length 1.1.

The inradius of this equilateral triangle is 36.\dfrac{\sqrt3}{6}. The area of the circle is then π(36)2=π12. \pi \cdot \left(\dfrac{\sqrt3}{6}\right)^2 = \dfrac{\pi}{12}.

Let OO be the center of the larger circle. Drop the perpendicular from OO to GH\overline{GH} at J.J. Draw OG.\overline{OG}.

We have that OJG\triangle OJG is right. Since HGI=60,\angle HGI = 60^{\circ}, we also have that OJG\triangle OJG is a 30609030-60-90 triangle.

Let OJ=r.OJ = r. Then OG=2r.OG = 2r. We also have that OGOG is the sum of the height of the hexagon, equilateral triangle, and radius of the circle.

Then OG=32+3+r. OG = \dfrac{\sqrt3}{2} + \sqrt3 + r.

Substituting in OG,OG, we get 2r=32+3+r. 2r = \dfrac{\sqrt3}{2} + \sqrt3 + r. Simplifying gives us r=332. r = \dfrac{3\sqrt3}{2}.

The area of the larger circle is then π(332)2=274π. \pi \cdot \left(\dfrac{3\sqrt3}{2}\right)^2 = \dfrac{27}{4}\pi.

The desired ratio is then 27π4π12=81. \dfrac{\frac{27\pi}{4}}{\frac{\pi}{12}} = 81.

Thus, D is the correct answer.

21.

A palindrome between 10001000 and 10,00010,000 is chosen at random. What is the probability that it is divisible by 7?7?

110\dfrac{1}{10}

19\dfrac{1}{9}

17\dfrac{1}{7}

16\dfrac{1}{6}

15\dfrac{1}{5}

Answer: E
Solution:

Note that we can express any 44 digit number as abcd.abcd. This can be expressed in long form as 103a+102b+10c+d. 10^3a + 10^2b + 10c + d. Since in a palindrome, we have that a=da = d and b=c.b = c. We can simplify this to get 1001a+110b. 1001a + 110b. Note that 10011001 is divisible by 7.7. This means that 110b110b must also be divisible by 7.7.

The only way for this to happen is if bb is 00 or 77 since 110110 is not divisible by 7.7.

There are 99 options for aa and 22 options for b,b, for a total of 92=189 \cdot 2 = 18 palindromes.

The total number of palindromes is 9109 \cdot 10 since there are 99 options for the thousands digit and 1010 options for the hundreds digit.

The desired probability is then 18910=15. \dfrac{18}{9 \cdot 10} = \dfrac{1}{5}.

Thus, E is the correct answer.

22.

Seven distinct pieces of candy are to be distributed among three bags. The red bag and the blue bag must each receive at least one piece of candy; the white bag may remain empty. How many arrangements are possible?

19301930

19311931

19321932

19331933

19341934

Answer: C
Solution:

We can count this with complementary counting. The total number of ways to distribute the candies with no restrictions is 37=2187. 3^7 = 2187.

To find the number of invalid arrangements, we have to count the number of ways where either the red or blue bag is empty.

For the case where the red bag is empty, each candy has 22 options for the bag that goes into. There are then 27=128 2^7 = 128 arrangements for this case. Similarly, there are 128128 arrangements for the case where the blue bag is empty.

There is an overlap of one case where both bags are empty. The final answer is then 2187(128+1281)=1932. 2187 - (128 + 128 - 1) = 1932.

Thus, C is the correct answer.

23.

The entries in a 3×33 \times 3 array include all the digits from 11 through 9,9, arranged so that the entries in every row and column are in increasing order. How many such arrays are there?

1818

2424

3636

4242

6060

Answer: D
Solution:

Note that 11 and 99 must be in the top left and bottom right corners respectively. We must also have that 22 and 88 are next to these squares.

We can then case on the center square. Note that the only possible values are 4,4,5,5, or 6.6.

Case 1: the center is 44

The 33 is necessarily next to the 1,1, since there is no other option that is less than 4.4.

Any number can be in the square next to the 8,8, but the other two squares are then fixed. There are 223=12 2 \cdot 2 \cdot 3 = 12 cases (two places for the 2,2, two places for the 8,8, and three choices for the square adjacent to 88).

Case 2: the center is 55

We can case on the position of the 3.3. If the 33 is in the top right square, the 44 is necessarily next to the 1.1.

If the 88 is above the 9,9, then the other two squares are fixed. If it is to the left of the 9,9, the other two squares can be filled arbitrarily.

Now consider when the 33 is below the 1.1. There are two spots for the 8,8, and the square next to the 88 can be any number.

The other two squares are then fixed. This means that this case has a total of 2(1+2+23)=18. 2(1 + 2 + 2 \cdot 3) = 18. We multiply by two since the 22 can be either to the right of or below the 1.1.

Case 3: the center is 66

This is similar to case 11 since the 77 is fixed instead of the 3.3.

The total number of arrangements is then 12+18+12=42. 12 + 18 + 12 = 42.

Thus, D is the correct answer.

24.

A high school basketball game between the Raiders and Wildcats was tied at the end of the first quarter. The number of points scored by the Raiders in each of the four quarters formed an increasing geometric sequence, and the number of points scored by the Wildcats in each of the four quarters formed an increasing arithmetic sequence. At the end of the fourth quarter, the Raiders had won by one point. Neither team scored more than 100100 points. What was the total number of points scored by the two teams in the first half?

3030

3131

3232

3333

3434

Answer: E
Solution:

Let aa be the number of points scored in the first quarter. Let rr be the common ratio for the Raiders and dd the difference for the Wildcats.

First, we can establish that rr is an integer. Assume for the sake of contradiction that it is not and r=mnr = \frac{m}{n} where gcd(m,n)=1.\gcd(m, n) = 1.

For ar,ar2,ar, ar^2, and ar3ar^3 to all be integers, we must have that n,n2,n, n^2, and n3n^3 divide a.a. We can then let a=n3ka = n^3k for some integer k.k.

Then we have that k(n3+n2m+nm2+m3)<100 k\left(n^3 + n^2m + nm^2 + m^3\right) \lt 100

Minimizing nn and k,k, we can assume that n=2n = 2 and k=1.k = 1. This gives us m<4,m \lt 4, which means that r=32.r = \dfrac{3}{2}.

Testing out this value shows that it does not work. Since this value does not work, no other non-integer rational ratio will work. This means rr is integral.

Then the sum of the quarter scores for the Wildcats is a+(a+d)+(a+2d)+(a+3d) a + (a + d) + (a + 2d) + (a + 3d) =4a+6d. = 4a + 6d.

We must have that a(1+r+r2+r3)= a(1 + r + r^2 + r^3) = 4a+6d+1. 4a + 6d + 1.

Trying out values, let r=2.r = 2. Then we have 15a=4a+6d+1, 15a = 4a + 6d + 1, which simplifies to 11a=6d+1. 11a = 6d + 1.

Looking for the smallest multiple of 1111 that leaves a remainder of 11 when divided by 6,6, we get 55.55.

With this value, we get a=5a = 5 and d=9.d = 9. The sum of the scores of the first two quarters for both teams is 5+10+5+14=34. 5 + 10 + 5 + 14 = 34.

Thus, E is the correct answer.

25.

Let a>0,a \gt 0, and let P(x)P(x) be a polynomial with integer coefficients such that P(1)=P(3)=P(5)=P(7)=a,P(1) = P(3) = P(5) = P(7) = a, and P(2)=P(4)=P(6)=P(8)P(2) = P(4) = P(6) = P(8) =a.= -a. What is the smallest possible value of a?a?

105105

315315

945945

7!7!

8!8!

Answer: B
Solution:

We can define a new function Q(x)=P(x)a Q(x) = P(x) - a so that QQ has roots at 1,3,5,1, 3, 5, and 7.7. Then we can factor QQ to get Q(x)=(x1)(x3)(x5) Q(x) = (x - 1)(x - 3)(x - 5)(x7)(x).(x - 7)(x).

We can plug in the values of 2,4,6,2, 4, 6, and 88 to get R(2)=(21)(23)(25) R(2) = (2 - 1)(2 - 3)(2 - 5) (27)Q(2)=15Q(2)=2a (2 - 7)Q(2) = -15Q(2) = -2a And R(4)=(41)(43)(45) R(4) = (4 - 1)(4 - 3)(4 - 5)(47)Q(4)=9Q(4)=2a(4 - 7)Q(4) = 9Q(4) = -2a And R(6)=(61)(63)(65) R(6) = (6 - 1)(6 - 3)(6 - 5)(67)Q(6)=15Q(6)=2a(6 - 7)Q(6) = -15Q(6) = -2a And R(8)=(81)(83)(85) R(8) = (8 - 1)(8 - 3)(8 - 5) (87)Q(8)=105Q(8)=2a (8 - 7)Q(8) = 105Q(8) = -2a

To minimize a,a, we can set a=lcm(15,9,15,105).a = \text{lcm}(15, 9, 15, 105). Then a=315.a = 315.

Thus, B is the correct answer.