¹₉ of the people at a museum were boys. 70% of the remaining people were girls and the rest were adults. The number of girls was 187 more than the total number of boys and adults. After some girls left the museum, 50% of the people that remained were girls. How many girls left the museum?

Boys	Adults	Girls	Total
1x5	8x5		9x5
	3x4	7x4
5	12	28	45

	Boys and adults	Girls
Before	17x1 = 17 u	28x1 = 28 u
Change		- 11 u
After	1x17 = 17 u	1x17 = 17 u

70% = ⁷⁰₁₀₀ = ⁷₁₀
Adults : Girls = 3 : 7

The total number of adults and girls at first is repeated.  Make the total number of adults at first the same. LCM of 8 and 10 is 40.

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 17 and 1 is 17.

The number of girls was 187 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
= 28 u - 17 u
= 11 u

11 u = 187

1 u = 187 ÷ 11 = 17

Number of girls who left the museum
= 28 u - 17 u
= 11 u
= 11 x 17
= 187

Answer(s): 187