Answer:
20:21
Explanation:
Let's first start by converting each ratio so that the number of girls is the same
2:3
4:7
The least common multiple of 3 and 4 is 12 so...
8:12
12:21
We add 8 and 12 to get the number of junior members...
8+12=20
Then we put it in a ratio with the amount of adult members...
20:21