The ratio of boys and girls in a class was 11:13. 8 girls and 4 boys join the class from this academic year and the ratio becomes 4:5. Find the strength of the class.

A. 96
B. 68
C. 72
D. 108

Let the number of boys and girls in the class be 11x and 13x. 4 boys and 8 girls join the class. Strength of the class
= 11x+13x+4+8
= 24x+12 (11x+4):(13x+8) = 4:5 5*(11x+4)=4*(13x+8) 55x+20=52x+32 3x=12 x=4 24x+12=108