In a school, 0.9 of the girls and 0.3 of the boys take part in sports. There is an equal number of boys and girls who do not take part in sports. If 660 students take part in sports, how many less students 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
9x7	1x7	3	7
	1x7		1x7
63 u	7 u	3 u	7 u

0.9 = ⁹₁₀
Girls that take part : Girls that do not take part = 9 : 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 students who take part in sports
= 63 u + 3 u
= 66 u

66 u = 660

1 u = 660 ÷ 66 = 10

Number of students who do not take part in sports
= 7 u + 7 u
= 14 u

Number of less students who do not take part in sports than those who take part in sports
= 66 u - 14 u 
= 52 u
= 52 x 10
= 520

Answer(s): 520