SSC CHSL Model Paper 13

Number of boys in college A = $\frac{4}{9}\times$ 20% of 1800 $=\frac{4}{9}\times \frac{20}{100}\times 1800=160$
Number of girls in college A $=\frac{5}{9}\times$ 20% of 1800 $=\frac{5}{9}\times \frac{20}{100}\times 1800=200$
Number of boys in college B = $\frac{1}{3}\times$ 18% of 1800 $=\frac{1}{3}\times \frac{18}{100}\times 1800=108$
Number of girls in college B = $\frac{2}{3}\times$ 18% of 1800 $=\frac{2}{3}\times \frac{18}{100}\times 1800=216$
Required ratio $=\frac{160+108}{200+216}=\frac{268}{416}=\frac{67}{104}$