Answer:
4:5
Explanation:
Since there are 16 girls and 20 boys, the ratio would be 16:20. Since you are wanting it in simplest form, you will divide until you can't divide any more. But what you do to the one side, you have to do to the other.
16/2=8
20/2=10
8/2=4
10/2=5
You can't divide anymore because 5 is odd. So the answer is 4:5