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

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

Problem: the average of first 17 even numbers is ?
18

Problem: two pipes a and b can separately fill a cistern in 60 minutes and 80 minutes respectively . there is a third pipe in the bottom of the cistern to empty it . if all the three pipes are simultaneously opened , then the cistern is full in 40 minutes . in how much time , the third pipe alone can empty the cistern ?

240 min