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.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

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
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 d−6d-6 rainy mornings and d−5d-5 rainy afternoons. By condition (2),(2), these are distinct rainy occasions, and their total is 7.7. Hence (d−6)+(d−5)=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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