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

[Q]: Problem: a sum of money at simple interest amounts to rs . 815 in 3 years and to rs . 878 in 4 years . the sum is :
[A]: 626

[Q]: Problem: in how many no . between 10 and 30 exactly two of the digits is 2 ?
[A]: 1

[Q]: Problem: a bus trip of 550 miles would have taken 1 hour less if the average speed v for the trip had been greater by 5 miles per hour . what was the average speed v , in miles per hour , for the trip ?
[A]:
50