The average (arithmetic mean) of all scores on a certain algebra test was 90. If the average of the 8 male students’ grades was 84, and the average of the female students’ grades was 92, how many female students took the test?
Answers:
A) 8
B) 9
C) 10
D) 21
E) 24

Rationale: "total marks of male = m total marks of female = f number of males = 8 number of females = f given : ( m + f ) / ( 8 + f ) = 90 - - - - - - - - - - - - - 1 also given , m / 8 = 84 thus m = 672 - - - - - - - - - 2 also , f / f = 92 thus f = 92 f - - - - - - - - - 3 put 2 and 3 in 1 : we get ( 672 + 92 f ) / ( 8 + f ) = 90 solving this we get f = 24 ans : e"
Answer: E