2002 AMC 10B Problems/Problem 8

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Problem

Suppose July of year $N$ has five Mondays. Which of the following must occurs five times in the August of year $N$ ? (Note: Both months have $31$ days.)

$\textbf{(A)}\ \text{Monday} \qquad \textbf{(B)}\ \text{Tuesday} \qquad \textbf{(C)}\ \text{Wednesday} \qquad \textbf{(D)}\ \t...$

Solution

If there are five Mondays, there are only three possibilities for their dates: $(1,8,15,22,29)$ , $(2,9,16,23,30)$ , and $(3,10,17,24,31)$ .

In the first case August starts on a Thursday, and there are five Thursdays, five Fridays, and five Saturdays in August.

In the second case August starts on a Wednesday, and there are five Wednesdays, five Thursdays, and five Fridays in August.

In the third case August starts on a Tuesday, and there are five Tuesdays, five Wednesdays, and five Thursdays in August.

The only day of the week that is guaranteed to appear five times is therefore $\boxed{\textbf{(D)}\ \text{Thursday}}$ .

2002 AMC 10B (Problems • Resources)
Preceded by Problem 7	Followed by Problem 9
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25

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2002 AMC 10B Problems/Problem 8

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