²₉ of the people at a tourist attraction were girls. 70% of the remaining people were boys and the rest were adults. The number of boys was 128 more than the total number of girls and adults. After some boys left the tourist attraction, 50% of the people that remained were boys. How many boys left the tourist attraction?

Girls	Adults	Boys	Total
2x10	7x10		9x10
	3x7	7x7
20	21	49	90

	Girls and adults	Boys
Before	41x1 = 41 u	49x1 = 49 u
Change		- 8 u
After	1x41 = 41 u	1x41 = 41 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 7 and 10 is 70.

50% = ⁵⁰₁₀₀ = ¹₂

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 41 and 1 is 41.

The number of boys was 128 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
= 49 u - 41 u
= 8 u

8 u = 128

1 u = 128 ÷ 8 = 16

Number of boys who left the tourist attraction
= 49 u - 41 u
= 8 u
= 8 x 16
= 128

Answer(s): 128