In a school, 0.5 of the boys and 0.7 of the girls take part in quizzes. There is an equal number of girls and boys who do not take part in quizzes. If 170 pupils take part in quizzes, how many less pupils do not take part in quizzes than those who take part in quizzes?

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 take part in quizzes
= 3 u + 7 u
= 10 u

10 u = 170

1 u = 170 ÷ 10 = 17

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

Number of less pupils who do not take part in quizzes than those who take part in quizzes
= 10 u - 6 u 
= 4 u
= 4 x 17
= 68

Answer(s): 68