²₉ of the people at a park were boys. 90% of the remaining people were girls and the rest were adults. The number of girls was 216 more than the total number of boys and adults. After some girls left the park, 50% of the people that remained were girls. How many girls left the park?

Boys	Adults	Girls	Total
2x10	7x10		9x10
	1x7	9x7
20	7	63	90

	Boys and adults	Girls
Before	27x1 = 27 u	63x1 = 63 u
Change		- 36 u
After	1x27 = 27 u	1x27 = 27 u

90% = ⁹⁰₁₀₀ = ⁹₁₀
Adults : Girls = 1 : 9

The total number of adults and girls at first is repeated.  Make the total number of adults at first the same. LCM of 7 and 10 is 70.

50% = ⁵⁰₁₀₀ = ¹₂

When some girls left, the total number of boys and adults remains unchanged. Make the total number of boys and adults the same. LCM of 27 and 1 is 27.

The number of girls was 216 more than the total number of boys and adults at first.

Number of more girls than the total number of boys and adults at first
= 63 u - 27 u
= 36 u

36 u = 216

1 u = 216 ÷ 36 = 6

Number of girls who left the park
= 63 u - 27 u
= 36 u
= 36 x 6
= 216

Answer(s): 216