1994 AMC 8 Problem 10

Attempt Problem 10 of the 1994 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1994 AMC 8 solutions, or check the answer key.

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10.

For how many positive integer values of NN (N>0)(N \gt 0) is the expression

36N+2\frac{36}{N+2}

an integer?

77

88

99

1010

1212

Answer: A
Concepts:divisibilityfactor
Difficulty rating: 860
Small Hint:

36N+2\dfrac{36}{N+2} is an integer exactly when N+2N+2 is a divisor of 3636

Big Hint:

Since N>0,N \gt 0, only divisors of 3636 that are greater than 22 count

Solution:

The expression is an integer when N+2N+2 divides 36.36. The divisors of 3636 are 1,1, 2,2, 3,3, 4,4, 6,6, 9,9, 12,12, 18,18, 36.36.

Because N>0,N \gt 0, we need N+2>2,N + 2 \gt 2, leaving the divisors 3,3, 4,4, 6,6, 9,9, 12,12, 18,18, 3636: that is 77 values.

Thus, the correct answer is A .

Problem 9#9
Full Exam

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