Three fifths of the children in a school are boys. 7/8 of the girls in the school are right-handed. What fraction of the children in the school are left-handed girls

To find the answer we only need to know,

Total no.of girls and Total no.of right handed girls.

So,

Total no.of right handed girls = 7/8

Total no.of girls                        = 8/8 (as given in question)

Total no.of left handed girls is,

(Fraction of total no.of girls) - (Fraction of total no.of left handed girls)

= 8/8 - 7/8

= 1/8

∴ 1/8 of the girls in the school are left handed.