In a school, 0.5 of the boys and 0.7 of the girls take part in competitions. There is an equal number of girls and boys who do not take part in competitions. If 90 children do not take part in competitions, how many more children take part in competitions than those who do not take part in competitions?

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 children who do not take part in competitions
= 3 u + 3 u
= 6 u

6 u = 90

1 u = 90 ÷ 6 = 15

Number of children who take part in competitions
= 3 u + 7 u
= 10 u

Number of more children who take part in competitions than those who do not take part in competitions
= 10 u - 6 u
= 4 u
= 4 x 15
= 60

Answer(s): 60