In a school, 0.8 of the boys and 0.1 of the girls take part in competitions. There is an equal number of girls and boys who do not take part in competitions. If 481 children take part in competitions, how many less children do not take part in competitions than those who take part in competitions?

Boys		Girls
Take part	Do not take part	Take part	Do not take part
4x9	1x9	1	9
	1x9		1x9
36 u	9 u	1 u	9 u

0.8 = ⁴₅
Boys that take part : Boys that do not take part = 4 : 1

0.1 = ¹₁₀
Girls that take part : Girls that do not take part = 1 : 9

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 9 is 9.

Number of children who take part in competitions
= 36 u + 1 u
= 37 u

37 u = 481

1 u = 481 ÷ 37 = 13

Number of children who do not take part in competitions
= 9 u + 9 u
= 18 u

Number of less children who do not take part in competitions than those who take part in competitions
= 37 u - 18 u 
= 19 u
= 19 x 13
= 247

Answer(s): 247