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

[EX Q]: Problem: two pipes a and b can separately fill a cistern in 60 minutes and 75 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 50 minutes . in how much time , the third pipe alone can empty the cistern ?
[EX A]: 100 min

[EX Q]: Problem: how many numbers between 400 and 1000 can be made with the digits 2 , 3,4 , 5,6 and 0 ?
[EX A]: 60

[EX Q]: Problem: a man took a loan at rate of 12 % per annum simple interest . after 3 years he had to pay 7200 interest . the principal amount borrowed by him was .
[EX A]:
rs 20000