Nora's school organized a trip to Australia. At first, the ratio of the number of girls to the number of boys who planned to participate in the trip was 7 : 5. On the day of registration, 39 boys decided to withdraw and 39 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 Australia in the end?

	Girls	Boys	Total
Before	7x5 = 35 u	5x5 = 25 u	12x5 = 60 u
Change	+ 13 u	- 13 u
After	4x12 = 48 u	1x12 = 12 u	5x12 = 60 u

20% = ²⁰₁₀₀ = ¹₅

Since 39 boys withdrew and another 39 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 12 and 5 is 60.

Number of boys who decided to withdraw
= 25 u - 12 u
= 13 u

13 u = 39

1 u = 39 ÷ 13 = 3

Number of less boys than girls in the end
= 48 u - 12 u
= 36 u
= 36 x 3
= 108

Answer(s): 108