2010 AMC 10A Problem 10

Below is the professionally curated solution for Problem 10 of the 2010 AMC 10A, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2010 AMC 10A solutions, or check the answer key.

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Concepts:date and timemodular arithmetic

Difficulty rating: 1480

10.

Marvin had a birthday on Tuesday, May 27 in the leap year 2008.2008. In what year will his birthday next fall on a Saturday?

20112011

20122012

20132013

20152015

20172017

Solution:

Note that on a normal year, we have that 365=527+1, 365 = 52 \cdot 7 + 1, which means that for a specific day, it moves to the day after the next year.

On a leap year, the day of the week moves forward two since there is an extra day.

Then in 2009,2009, this day falls on a Wednesday. In 2010,2010, it falls on a Thursday.

Similarly, in 2011,2011, it falls on a Friday. In 2012,2012, however, since it is a leap year, it falls on a Sunday.

Now, for the next three years, the day moves forward one. Then in 2016,2016, it moves forward two, landing on a Friday.

Finally, in 2017,2017, the day of the week is a Saturday.

Thus, E is the correct answer.

Problem 10 in Other Years