In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[Q]: Problem: if a - b = 5 and a 2 + b 2 = 31 , find the value of ab .
Options: a ) 9 , b ) 2 , c ) 3 , d ) 7 , e ) 12
[A]: c

[Q]: Problem: the average marks of a class of 40 students is 44 and that of another class of 45 students is 70 . find the average marks of all the students ?
Options: a ) 52.6 , b ) 52.4 , c ) 52.1 , d ) 69.5 , e ) 52.9
[A]: d

[Q]: Problem: what is the total number of positive integers that are less than 500 and that have no positive factor in common with 500 other than 1 ?
Options: a ) 50 , b ) 100 , c ) 200 , d ) 300 , e ) 400
[A]:
c