Marvin had a birthday on Tuesday, May 27 in the leap year 2008. In what year will his birthday next fall on a Saturday? (A)2011(B)2012(C)2013(D)2015(E)2017
Official solution
(E)2017 There are 365 days in a non-leap year. There are 7 days in a week. Since 365=52⋅7+1 (or 365≡1(mod7)), the same date (after February) moves "forward" one day in the subsequent year, if that year is not a leap year. For example: 5/27/08 Tue 5/27/09 Wed However, a leap year has 366 days, and 366=52⋅7+2 . So the same date (after February) moves "forward" two days in the subsequent year, if that year is a leap year. For example: 5/27/11 Fri 5/27/12 Sun You can keep counting forward to find that the first time this date falls on a Saturday is in 2017: 5/27/13 Mon 5/27/14 Tue 5/27/15 Wed 5/27/16 Fri 5/27/17 Sat
Source: NuminaMath-1.5,
licensed Apache-2.0.
Statement and solution reproduced as published; topic, difficulty and ordering added
by this site.