¹₈ of the visitors at a tourist attraction were girls. 90% of the remaining visitors were boys and the rest were adults. The total number of girls and adults is 644 less than the number of boys. After some boys entered the tourist attraction, 80% of the visitors that remained were boys. How many boys entered the tourist attraction?

Girls	Adults	Boys	Total
1x10	7x10		8x10
	1x7	9x7
10	7	63	80

	Girls and adults	Boys
Before	17x1 = 17 u	63x1 = 63 u
Change		+ 5 u
After	1x17 = 17 u	4x17 = 68 u

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

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.

80% = ⁸⁰₁₀₀ = ⁴₅

When some boys entered, the total number of girls and adults remains unchanged. Make the total number of girls and adults the same. LCM of 17 and 1 is 17.

The total number of girls and adults is 644 less than the number of boys.

Number of less girls and adults than the number of boys at first
= 63 u - 17 u
= 46 u

46 u = 644

1 u = 644 ÷ 46 = 14

Number of boys who entered the tourist attraction
= 68 u - 63 u
= 5 u
= 5 x 14
= 70

Answer(s): 70