Problem:
On a trip from the United States to Canada, Isabella took U.S. dollars. At the border she exchanged them all, receiving 10 Canadian dollars for every 7 U.S. dollars. After spending 60 Canadian dollars, she had Canadian dollars left. What is the sum of the digits of ?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
Isabella received 10d/7 Canadian dollars at the border and spent 60 of them. Thus , from which it follows that , and the sum of the digits of is .
The problems on this page are the property of the MAA's American Mathematics Competitions