1959 AMC 12 Problem 46

Attempt Problem 46 of the 1959 AMC 12 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 1959 AMC 12 solutions, or check the answer key.

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46.

A student on vacation for dd days observed that

(1)(1) it rained 77 times, morning or afternoon;

(2)(2) when it rained in the afternoon, it was clear in the morning;

(3)(3) there were five clear afternoons;

(4)(4) there were six clear mornings.

Then dd equals:

77

99

1010

1111

1212

Answer: B
Concepts:basic countingcomplementary counting
Difficulty rating: 1590
Small Hint:

Count rainy mornings and rainy afternoons from the numbers of clear half-days

Big Hint:

Condition (2)(2) ensures that a rainy afternoon and rainy morning never occur on the same day

Solution:

There are d6d-6 rainy mornings and d5d-5 rainy afternoons. By condition (2),(2), these are distinct rainy occasions, and their total is 7.7. Hence (d6)+(d5)=7, (d-6)+(d-5)=7, so 2d=182d=18 and d=9.d=9.

Thus, the correct answer is B.

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Problem 46 in Other Years

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