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

[Q]: Problem: for any positive integer n , the sum of the first n positive integers equals n ( n + 1 ) / 2 . what is the sum of odd all the integers between 10 and 100 ?
[A]: 2475

[Q]: Problem: by selling an article for $ 195 , a person gains $ 45 . what is the gain % ?
[A]: 30 %

[Q]: Problem: pipe a can fill a tank in 6 hours . due to a leak at the bottom , it takes 10 hours for the pipe a to fill the tank . in what time can the leak alone empty the full tank ?
[A]:
15