The ratio of number of boys and girls in a class is 3 : 2. In the 1st semester exam 20% of boys and 25%
of girls get more than or equal to 90% marks. What percentage of students get less than 90% marks ?	Choose the correct choice from the following.
A) 56
B) 70
C) 78
D) 80
E) 85

Rationale: let boys = 3 x and girls = 2 x . number of those who get less than 90 % mark = ( 80 % of 3 x ) + ( 75 % of 2 x ) = ( 80 / 100 ) * 3 x + ( 75 / 100 * 2 x ) = 39 x / 10 required percentage = ( 39 x / 10 * 1 / 5 x * 100 ) % = 78 % . answer : c
Answer: C