In a school, 0.8 of the girls and 0.3 of the boys take part in competitions. There is an equal number of boys and girls who do not take part in competitions. If 558 pupils take part in competitions, how many less pupils do not take part in competitions than those who take part in competitions?

Girls		Boys
Take part	Do not take part	Take part	Do not take part
4x7	1x7	3	7
	1x7		1x7
28 u	7 u	3 u	7 u

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

0.3 = ³₁₀
Boys that take part : Boys that do not take part = 3 : 7

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 7 is 7.

Number of pupils who take part in competitions
= 28 u + 3 u
= 31 u

31 u = 558

1 u = 558 ÷ 31 = 18

Number of pupils who do not take part in competitions
= 7 u + 7 u
= 14 u

Number of less pupils who do not take part in competitions than those who take part in competitions
= 31 u - 14 u 
= 17 u
= 17 x 18
= 306

Answer(s): 306