2006 AMC 10B Problems/Problem 16
Problem
Leap Day, February 29, 2004, occurred on a Sunday. On what day of the week will Leap Day, February 29, 2020, occur?
Solution
There are 
days in a year, plus 
extra day if there is a Leap Day, which occurs on years that are multiples of 4 (with a few exceptions that don't affect this problem).
Therefore, the number of days between Leap Day 2004 and Leap Day 2020 is:
Since the days of the week repeat every 
days and 
, the day of the week Leap Day 2020 occurs is the day of the week the day before Leap Day 2004 occurs, which is 
.
Solution (Feasible Shortcuts)
Since every non-leap year there is one day extra after the 
weeks, we can deduce that if we were to travel forward 
amount of non-leap years, then the answer would be "Sunday + " days.
However, we also have leap-years in our pool of years traveled forward, and for every leap-year that passes, we have two extra days after the 52 weeks. So we would travel "Sunday + 
" days.
Mixing these two together, we get 
leap years 
, and 
"normal years". We thus get 
"extra days" after Sunday. Since seven days are in a week, we can get 
, and six days after Sunday is .
See Also
| 2006 AMC 10B (Problems • Answer Key • Resources) | ||
| Preceded by Problem 15 |
Followed by Problem 17 | |
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| All AMC 10 Problems and Solutions | ||
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