You didn't specify the total number of students in the choir, but I can tell you this about estimating (especially when doing it mentally):
When you are estimating answers, it is easiest to use large, round numbers such as 25%. It is easy because it is the same as saying 1/4 of something. On the other hand, 24% would be 6/25 (in simplest form), which would be harder to calculate.
6 1/3 +2 3/8 = 17/24 so you have to subtract it from the 2 1/4 fluid to know the amount of dressing remaining and your answer should be negative which is -37/24.
