SOLUTION: of 300 children in school 60% are girls and 40% are boys.if 12 girls leave and no new pupils are admitted what percentage of the total will be boys and girls.

of 300 children in school 60% are girls and 40% are boys.if 12 girls leave and no new pupils are admitted what percentage of the total will be boys and girls.
Ans:
60% are girls. Therefore number of girls = 300*60% = 300*60/100 = 180
And number of boys = 300 - 180 = 120.
If 12 girls leave,
Number of girls = 180 - 12 = 168.
Number of boys = 120 (unchanged)
Total number of students = 288
%age of girls = (168/288)*100 = %
%age of boys = (120/288)* 100 = % 
(or it can be also computed as 100 - 58.33 = 41.67%)
Hope you got it :)