Sophia's school organized a trip to Fiji. At first, the ratio of the number of girls to the number of boys who planned to participate in the trip was 8 : 7. On the day of registration, 36 boys decided to withdraw and 36 more girls decided to join in. In the end, the number of boys who participated became 20% of the total children for the trip. How many less boys than girls would visit Fiji in the end?

	Girls	Boys	Total
Before	8x1 = 8 u	7x1 = 7 u	15x1 = 15 u
Change	+ 4 u	- 4 u
After	4x3 = 12 u	1x3 = 3 u	5x3 = 15 u

20% = ²⁰₁₀₀ = ¹₅

Since 36 boys withdrew and another 36 girls joined, the total number of children at first and in the end remains unchanged. Make the total number of children the same. LCM of 15 and 5 is 15.

Number of boys who decided to withdraw
= 7 u - 3 u
= 4 u

4 u = 36

1 u = 36 ÷ 4 = 9

Number of less boys than girls in the end
= 12 u - 3 u
= 9 u
= 9 x 9
= 81

Answer(s): 81