The task is to generate the correct answer for a given math problem.

[EX Q]: Problem: if the sides of a cube are in the ratio 5 : 3 . what is the ratio of their diagonals ?
[EX A]: 5 : 3'

[EX Q]: Problem: if the cost price of 50 articles is equal to the selling price of 40 articles , then the gain or loss percent is ?
[EX A]: 25 %

[EX Q]: Problem: a collection of books went on sale , and 2 / 3 of them were sold for $ 3.50 each . if none of the 40 remaining books were sold , what was the total amount received for the books that were sold ?
[EX A]:
$ 280