Ava's school organized a trip to Russia. 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, 63 boys decided to withdraw and 63 more girls decided to join in. In the end, the number of boys who participated became 30% of the total children for the trip. How many children would visit Russia in the end?

	Girls	Boys	Total
Before	7x5 = 35 u	5x5 = 25 u	12x5 = 60 u
Change	+ 7 u	- 7 u
After	7x6 = 42 u	3x6 = 18 u	10x6 = 60 u

30% = ³⁰₁₀₀ = ³₁₀

Since 63 boys withdrew and another 63 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 10 is 60.

Number of boys who decided to withdraw
= 25 u - 18 u
= 7 u

7 u = 63

1 u = 63 ÷ 7 = 9

Number of children that would visit Russia in the end
= 42 u + 18 u
= 60 u
= 60 x 9
= 540

Answer(s): 540