In a school, 0.5 of the boys and 0.7 of the girls take part in sports. There is an equal number of girls and boys who do not take part in sports. If 30 pupils do not take part in sports, how many more pupils take part in sports than those who do not take part in sports?

Boys		Girls
Take part	Do not take part	Take part	Do not take part
1x3	1x3	7	3
	1x3		1x3
3 u	3 u	7 u	3 u

0.5 = ¹₂
Boys that take part : Boys that do not take part = 1 : 1

0.7 = ⁷₁₀
Girls that take part : Girls that do not take part = 7 : 3

The number of girls who do not take part is repeated.  Make the number of girls who do not take part the same.  LCM of 1 and 3 is 3.

Number of pupils who do not take part in sports
= 3 u + 3 u
= 6 u

6 u = 30

1 u = 30 ÷ 6 = 5

Number of pupils who take part in sports
= 3 u + 7 u
= 10 u

Number of more pupils who take part in sports than those who do not take part in sports
= 10 u - 6 u
= 4 u
= 4 x 5
= 20

Answer(s): 20