Problem:
A triangular array of coins has coin in the first row, coins in the second row, coins in the third row, and so on up to coins in the th row. What is the sum of the digits of ?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
There are
coins in the array. Therefore . Because , it follows that . Indeed, , so and the sum of the digits of is .
The problems on this page are the property of the MAA's American Mathematics Competitions