Ava's school organized a trip to Norway. At first, the ratio of the number of boys to the number of girls who planned to participate in the trip was 7 : 5. On the day of registration, 70 girls decided to withdraw and 70 more boys decided to join in. In the end, the number of girls who participated became 30% of the total children for the trip. How many children would visit Norway in the end?

	Boys	Girls	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 70 girls withdrew and another 70 boys 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 girls who decided to withdraw
= 25 u - 18 u
= 7 u

7 u = 70

1 u = 70 ÷ 7 = 10

Number of children that would visit Norway in the end
= 42 u + 18 u
= 60 u
= 60 x 10
= 600

Answer(s): 600