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

[EX Q]: Problem: tourist purchased a total of 30 travelers checks in $ 50 and $ 100 denominations . the total worth of the travelers checks is $ 1800 . how many checks of $ 50 denominations can he spend so that average amount ( arithmetic mean ) of the remaining travelers checks is $ 100 ?
[EX A]: 2

[EX Q]: Problem: the volume of water inside a swimming pool doubles every hour . if the pool is filled to its full capacity within 8 hours , in how many hours was it filled to one quarter of its capacity ?
[EX A]: 6', 'e ) 7'

[EX Q]: Problem: a certain number when divided by 39 leaves a remainder 20 , what is the remainder when the same number is divided by 13 ?
[EX A]:
7