¹₉ of the people at a zoo were girls. 70% of the remaining people were boys and the rest were adults. The number of boys was 374 more than the total number of girls and adults. After some boys left the zoo, 60% of the people that remained were boys. How many boys left the zoo?

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

	Girls and adults	Boys
Before	17x2 = 34 u	28x2 = 56 u
Change		- 5 u
After	2x17 = 34 u	3x17 = 51 u

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

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

60% = ⁶⁰₁₀₀ = ³₅

When some boys left, the total number of girls and adults remains unchanged. Make the total number of girls and adults the same. LCM of 17 and 2 is 34.

The number of boys was 374 more than the total number of girls and adults at first.

Number of more boys than the total number of girls and adults at first
= 56 u - 34 u
= 22 u

22 u = 374

1 u = 374 ÷ 22 = 17

Number of boys who left the zoo
= 56 u - 51 u
= 5 u
= 5 x 17
= 85

Answer(s): 85