Question

On a trip from the United States to Canada, Isabella took d 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 d Canadian dollars left. What is the sum of the digits of d?

Answer 1

5

Explanation:

The exchange rate is 10 CAD = 7 USD

Which means:

10/7 CAD for EACH USD

So, d USD would be:

d * 10/7 = (10d)/7 CAD

This is what she has now, after exchange (in CAD).

She spends 60 and has "d" left, so finding d:

`(10d)/(7)-60=d\\(10d-420)/(7)=d\\10d-420=7d\\3d=420\\d=(420)/(3)\\d=140`

Hence, d = 140

The digits of d are 1, 4, and 0

The sum is:

1 + 4 + 0 = 5

The sum is 5