instruction:
The task is to generate the correct answer for a given math problem.
question:
Problem: if a - b = 5 and a 2 + b 2 = 31 , find the value of ab .
answer:
3


question:
Problem: find the sum the difference between the compound and s . i . on a certain sum of money for 5 years at 20 % per annum is rs . 75 of money ?
answer:
1875


question:
Problem: a start walking from a place at a uniform speed of 4 kmph in a particular direction . after half an hour , b starts from the same place and walks in the same direction as a at a uniform speed and overtakes a after 1 hour 48 minutes . find the speed of b .
answer:

4.6 kmph