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: for a certain exam , a score of 60 was 2 standard deviations below mean and a score of 100 was 3 standard deviations above mean . what was the mean score for the exam ? 
Options: a ) 74 , b ) 76 , c ) 78 , d ) 80 , e ) 82
[A]: b


[Q]: Problem: if the average ( arithmetic mean ) of a and b is 110 , and the average of b and c is 170 , what is the value of a − c ? 
Options: a ) − 120 , b ) − 100 , c ) 100 , d ) 135 , e ) it can not be determined from the information given
[A]: a


[Q]: Problem: in a group of cows and chickens , the number of legs was 20 more than twice the number of heads . the number of cows was : 
Options: a ) 5 , b ) 7 , c ) 10 , d ) 12 , e ) 14
[A]:
c