2011 AMC 8 真题
计时
40:00
1.
Margie 买了 个苹果,每个苹果 美分。她用一张 美元纸币付款。Margie 收到多少找零?
Margie bought apples at a cost of cents per apple. She paid with a -dollar bill. How much change did Margie receive?
答案:E
难度评级:370
解答:
苹果总共花了 美分,也就是 。因此 Margie 收到 美元找零。
所以正确答案是 E。
The apples cost a total of cents, which equals This means that Margie received dollars in change.
Thus, E is the correct answer.
2.
Karl 的长方形菜园是 英尺乘 英尺,Makenna 的菜园是 英尺乘 英尺。谁的菜园面积更大?
Karl's rectangular vegetable garden is feet by feet, and Makenna's is feet by feet. Whose garden is larger in area?
Karl 的菜园大 平方英尺。
Karl’s garden is larger by square feet.
Karl 的菜园大 平方英尺。
Karl’s garden is larger by square feet.
两个菜园一样大。
The gardens are the same size.
Makenna 的菜园大 平方英尺。
Makenna’s garden is larger by square feet.
Makenna 的菜园大 平方英尺。
Makenna’s garden is larger by square feet.
3.
一个正方形图案中有 块阴影方砖和 块非阴影方砖。若在该正方形周围加上一圈阴影方砖来扩展图案,扩展后阴影方砖与非阴影方砖的比是多少?
Extend the square pattern of shaded and unshaded square tiles by attaching a border of shaded tiles around the square. What is the ratio of shaded tiles to unshaded tiles in the extended pattern?
4.
下面是 Tyler 去年夏天九次外出钓到的鱼的数量: 关于平均数、中位数和众数,哪一个说法正确?
Here is a list of the numbers of fish that Tyler caught in nine outings last summer: Which statement about the mean, median, and mode is true?
中位数 < 平均数 < 众数
median < mean < mode
平均数 < 众数 < 中位数
mean < mode < median
平均数 < 中位数 < 众数
mean < median < mode
中位数 < 众数 < 平均数
median < mode < mean
众数 < 中位数 < 平均数
mode < median < mean
答案:C
解答:
为了更容易求这些值,先得到有序列表:
由此可知众数是 ,中位数是 ,平均数是 。
因为 ,所以有:
平均数 中位数 众数。
所以正确答案是 C。
To find these values more easily, we can get the following ordered list:
From this, we see that the mode is the median is and the mean is
Since we get that:
mean median mode.
Thus, C is the correct answer.
5.
从 年一月 日开始,经过 分钟后是什么时间?
What time was it minutes after the beginning of January
月一日晚上
January at PM
月一日晚上
January at PM
一月 日凌晨
January at AM
一月 日上午
January at AM
一月 日下午
January at PM
答案:D
解答:
除以 的余数是 。也就是说 ,所以 分钟等于 小时 分钟。
经过 小时到达一月 日,所以此时是 日当天开始后的 小时 分钟。
所以正确答案是 D。
The remainder when is divided by is This means that which means that minutes is the same as hours and minutes.
hours takes us to January so we get that we are hours and minutes into January
Thus, D is the correct answer.
6.
一个镇上有 名成年人,每个成年人拥有汽车、摩托车,或两者都有。若 名成年人拥有汽车, 名成年人拥有摩托车,那么有多少名汽车拥有者不拥有摩托车?
In a town of adults, every adult owns a car, a motorcycle, or both. If adults own cars and adults own motorcycles, how many of the car owners do not own a motorcycle?
答案:D
难度评级:870
解答:
已知有 人拥有摩托车,所以 人不拥有摩托车。
所以正确答案是 D。
We know that people own motorcycles, so people do not own motorcycles.
Thus, D is the correct answer.
7.
下列四个大的全等正方形分别被分成若干个全等三角形或长方形,并有部分区域被涂阴影。阴影面积占总面积的百分之多少?
Each of the following four large congruent squares is subdivided into combinations of congruent triangles or rectangles and is shaded. What percent of the total area is shaded?
答案:C
解答:
左上和右下的阴影区域各占所在正方形的四分之一。右上占八分之一,左下占八分之三。它们的总面积为
因此阴影区域合起来等于一个正方形的面积,占四个正方形总面积的 。
所以正确答案是 C。
The top left and the bottom right shaded regions are both a quarter of each square. The top right is one-eighth, and the bottom left is three-eights. Their combined area is
Therefore, the shaded regions combined equal the area of one square, so they are of the total area.
Thus, C is the correct answer.
8.
A 袋中有三枚分别标有 、、 的筹码。B 袋中有三枚分别标有 、、 的筹码。如果从每个袋中各取出一枚筹码,两枚筹码上的数字之和可能有多少个不同的值?
Bag A contains three chips labeled and Bag B contains three chips labeled and If one chip is drawn from each bag, how many different values are possible for the sum of the two numbers on the chips?
9.
Carmen 在一条多坡的公路上进行长途骑行。图像显示了她骑行过程中随时间变化的行驶英里数。Carmen 整个骑行的平均速度是多少英里每小时?
Carmen takes a long bike ride on a hilly highway. The graph indicates the miles traveled during the time of her ride. What is Carmen's average speed for her entire ride in miles per hour?
10.
Gotham City 的出租车在前 英里收费 ,之后每额外 英里收费 。你计划给司机 小费。用 最多可以乘坐多少英里?
The taxi fare in Gotham City is for the first mile and additional mileage charged at the rate for each additional mile. You plan to give the driver a tip. How many miles can you ride for ?
答案:C
解答:
小费固定为 ,从总额中减去后剩 。这大于 ,所以再减去前半英里的车费,并把 英里计入总距离。
现在还有 可用于额外里程。每 英里收费 ,等价于每 英里收费 。因此这笔钱还能乘坐 英里。总距离为 英里。
所以正确答案是 C。
There is a guaranteed tip, so we can subtract that from the total, leaving This is greater than so we can subtract that and add miles to the total distance.
We now have to use for additional miles. per mile is the same as for mile. That means one can ride for more miles with this much money. This leaves a total of miles.
Thus, C is the correct answer.
11.
图中显示一周内 Asha(左柱)和 Sasha(右柱)每天学习的分钟数。平均每天 Sasha 比 Asha 多学习多少分钟?
The graph shows the number of minutes studied by both Asha (left bar) and Sasha (right bar) in one week. On the average, how many more minutes per day did Sasha study than Asha?
答案:A
解答:
可以通过每天的差值来计算平均分钟数之差。
从星期一开始,Sasha 与 Asha 的差值分别为 、、、、。总差为 分钟,因此平均差为 。
所以正确答案是 A。
We can calculate the difference in average minutes by looking at the differences per day.
Starting with Monday, the differences between Sasha and Asha are and This is a total of minutes. Therefore, the average difference is
Thus, A is the correct answer.
12.
Angie、Bridget、Carlos 和 Diego 随机坐在一张方桌四周,每边坐一个人。Angie 和 Carlos 坐在相对两边的概率是多少?
Angie, Bridget, Carlos, and Diego are seated at random around a square table, one person to a side. What is the probability that Angie and Carlos are seated opposite each other?
答案:B
解答:
设 Angie 的座位已经确定。Carlos 等可能坐在另外 个座位中的任意一个,但其中只有一个座位与 Angie 相对。因此概率为 。
所以正确答案是 B。
Consider that Angie's seat is chosen. Carlos has an equal probability of being in any of the other seats. Only one of them is opposite Angie, however. Therefore, the probability is
Thus, B is the correct answer.
13.
两个全等正方形 和 的边长均为 。它们重叠形成图中所示的 乘 长方形 。长方形 的面积中有百分之多少被涂阴影?
Two congruent squares, and have side length They overlap to form the by rectangle shown. What percent of the area of rectangle is shaded?
14.
Colfax Middle School 有 名学生,男生与女生的比为 。Winthrop Middle School 有 名学生,男生与女生的比为 。两所学校举办舞会,所有学生都参加。舞会上女生占学生总数的几分之几?
There are students at Colfax Middle School, where the ratio of boys to girls is There are students at Winthrop Middle School, where the ratio of boys to girls is The two schools hold a dance and all students from both schools attend. What fraction of the students at the dance are girls?
15.
乘积 有多少位数字?
How many digits are in the product
16.
设 为边长 和 的三角形面积。设 为边长 和 的三角形面积。 与 有什么关系?
Let be the area of the triangle with sides of length and Let be the area of the triangle with sides of length and What is the relationship between and
答案:C
解答:
因为这些三角形是等腰三角形,可以作高,把它们分成如图所示的两个全等直角三角形。
用勾股定理,面积为 的三角形的高为 类似地,面积为 的三角形的高为
因此 同样
所以 。
所以正确答案是 C。
Since these triangles are isosceles, we can drop altitudes to create two congruent right triangles as shown in the diagram.
Using the Pythagorean theorem, we get that the altitude of the triangle with area equals Similarly, we get that the altitude of the triangle with area equals
With these altitudes, we can calculate the areas of the triangles. We get that Similarly,
Therefore,
Thus, C is the correct answer.
17.
设 、、、 为整数。若 那么 等于多少?
Let and be whole numbers. If then what does equal?
答案:A
难度评级:1140
解答:
为了找到所需指数,注意所有底数都是质数。因此质因数分解会有帮助。
有
由此可知 、、 且 ,其中 使 这一项等于 。
代入这些指数可得
所以正确答案是 A。
To find the desired exponents, note that all the bases are prime numbers. This means that finding the prime factorization will be helpful.
We get that
From this, it is clear that and ( since that makes the term equal ).
Therefore,
Thus, A is the correct answer.
18.
一枚公平的六面骰子掷两次。第一次掷出的数大于或等于第二次掷出的数的概率是多少?
A fair six-sided die is rolled twice. What is the probability that the first number that comes up is greater than or equal to the second number?
答案:D
解答:
掷骰子两次时有 类结果:第一次大于第二次、两次相等、第一次小于第二次。第一类和第三类由于对称而概率相同。
第二类发生的概率是 ,因为第一次可以是任意数,而第二次必须等于第一次。其余两类的总概率为。因此每一类的概率为。
所求概率是第一类加第二类,共为。
所以正确答案是 D。
There are possible outcomes when rolling a die twice: the first number is greater than the second, both numbers are equal, or the first number is less than the second number. The first and third outcomes have the same probability since they are symmetric.
The second outcome has a chance of happening, since the first number can be anything, and the second number must equal the first number. The other two outcomes have a combined probability of This means that each outcome has a chance of happening.
The desired probability is the first outcome plus the second outcome, for a total probability of
Thus, D is the correct answer.
19.
这个图形中有多少个长方形?
How many rectangles are in this figure?
20.
四边形 是梯形,、、,高为 。这个梯形的面积是多少?
Quadrilateral is a trapezoid, and the altitude is What is the area of the trapezoid?
21.
学生们猜 Norb 的年龄分别是 和 。Norb 说:“你们中至少一半猜得太低,有两个人只差一岁,而且我的年龄是质数。”Norb 多少岁?
Students guess that Norb's age is and Norb says, "At least half of you guessed too low, two of you are off by one, and my age is a prime number." How old is Norb?
答案:C
解答:
陈述的第一部分表示 Norb 的年龄大于 。
第二部分表示 Norb 的年龄要么在 和 之间,要么在 和 之间。
因为 是质数而 不是,所以 Norb 的年龄是 。
所以正确答案是 C。
The first part of the statement means that Norb's age is greater than
The second part means that Norb's age is either between and or between and
Since is prime and is not, Norb's age is
Thus, C is the correct answer.
22.
的十位数字是什么?
What is the tens digit of
23.
有多少个 -位正整数满足:四个数字互不相同,首位不是零,该整数是 的倍数,并且 是最大的数字?
How many -digit positive integers have four different digits, where the leading digit is not zero, the integer is a multiple of and is the largest digit?
答案:D
解答:
一个数能被 整除,个位数字必须是 或 。
如果个位数字是 ,另外三位中必须有一位是 。剩下两位必须从 中选择。有 种方式选这两个数字,并有 种方式排列这三位数字,共 个数。
如果个位数字是 ,千位数字有 种选择。选定千位后,另外 位共有 种选择和排列方式。因此此情况共有 个数。
合并两种情况,总数为 。
所以正确答案是 D。
For a number to be divisible by the units digit must be either or
If the units digit is one of the other three digits must be The remaining two digits must be chosen from There are ways to choose the pair, and there are ways to arrange the three digits for a total of numbers.
If the units digit is there are ways to choose the thousands digit. There are ways to choose the other digits. This leaves a total of numbers for this case.
Combining both cases, we get the total number of such integers is
Thus, D is the correct answer.
24.
可以用多少种方式写成两个质数之和?
In how many ways can be written as the sum of two primes?
答案:A
解答:
两个数相加得到奇数时,一个必须是奇数,另一个必须是偶数。唯一的偶质数是 ,所以另一个数只能是 。但 不是质数,因此 不能写成两个质数之和。
所以正确答案是 A。
For two numbers to add to an odd number, one of them must be odd and the other even. Thus the only even prime is so the other number is forced to be is not prime, however, so cannot be written as the sum of two primes.
Thus, A is the correct answer.
25.
一个半径为 的圆内切于一个正方形,并外接于另一个正方形,如图所示。圆内阴影面积与两个正方形之间阴影面积的比,最接近下列哪个分数?
A circle with radius is inscribed in a square and circumscribed about another square as shown. Which fraction is closest to the ratio of the circle's shaded area to the shaded area between the two squares?
答案:A
解答:
圆内阴影面积等于圆面积减去小正方形面积。内正方形的边长可由勾股定理求得:
因此内正方形面积为 。圆内阴影面积为 。
外正方形面积为 ,所以两个正方形之间的阴影面积为 。
所求比值为
所以正确答案是 A。
The circle's shaded area is equal to the area of the circle minus the area of the smaller square. The side length of the inner square can be calculated using the Pythagorean Theorem to get
Therefore, the area of the inner square is The circle's shaded area is then
The area of the outside square is so the shaded area between the two squares is
The desired fraction is
Thus, A is the correct answer.