Answer:
If you are rounding to the nearest tens the smallest number is 45. If you are rounding to the nearest whole number, the smallest number is 49.5
It wouldnt be an even number but i got 7.3
There are 81 girls to every 72 boys in total, which can be represented by 81/72, which put into decimal form, is 1.125. If you then take the number of boys in the group, 16, and multiply it by this number (because the problem states that the ratio is constant) you can find the number of girls in the group.
16*1.125=18
So there are 18 girls in a group with 16 boys.
