2016 AMC 12B Problem 5

Attempt Problem 5 of the 2016 AMC 12B 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 2016 AMC 12B solutions, or check the answer key.

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

5.

The War of 18121812 started with a declaration of war on Thursday, June 18,18, 1812.1812. The peace treaty to end the war was signed 919919 days later, on December 24,24, 1814.1814. On what day of the week was the treaty signed?
Friday
Saturday
Sunday
Monday
Tuesday
Answer: B
Concepts:modular arithmeticdate and time
Small hint:
Days of the week repeat every 77 days, so reduce 919919 modulo 77
Big hint:
919=7⋅131+2,919=7\cdot131+2, so count 22 days forward from Thursday
Solution:
Because 919=7⋅131+2,919=7\cdot131+2, the treaty was signed 131131 full weeks plus 22 days after Thursday. Two days beyond Thursday is Saturday.
Thus, the correct answer is B.
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