Problem: A student on vacation for d days observed that (1) it rained 7 times, morning or afternoon (2) when it rained in the afternoon, it was clear in the morning (3) there were five clear afternoons (4) there were six clear mornings. Then d equals:
Answer Choices:
A. 7
B. 9
C. 10
D. 11
E. 12
Solution:
Rainy AfternoonsNon-Rainy AfternoonsRainy MorningsacNon-Rainy Morningsbe
d=a+b+c+e a+b+c=7 a=0
c+e=5 b+e=6 ∴ e=2 ∴ d=9