Hey, the answer is 39.7142857143. But since we can't have half or less of a whole kid the number can be rounded up to 40. So there would be approximately 40 kids in each of the 7 groups. I solved this by dividing 278 by 7. If you do not know how to round all you do is take the number past the decimal on the right, and see if that number is more than five, if it is then change the number to the left of the decimal to one number higher that is how 39.7142857143 became simply 40.
Hope this Helps!:)
(If you need more help with rounding i would be more than happy to help you out my friend)