In a school, 0.5 of the girls and 0.7 of the boys take part in sports. There is an equal number of boys and girls who do not take part in sports. If 50 children take part in sports, how many less children do not take part in sports than those who take part in sports?

Girls		Boys
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
Girls that take part : Girls that do not take part = 1 : 1

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

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

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

10 u = 50

1 u = 50 ÷ 10 = 5

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

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

Answer(s): 20