Problem:
Of the balls in a large bag, are red and the rest are blue. How many of the red balls must be removed from the bag so that of the remaining balls are red?
Answer Choices:
A.
B.
C.
D.
E.
Solution:
The number of blue balls in the bag is of , which is . After some red balls are removed, the blue balls must be , or , of the number in the bag. There must be balls in the bag, so red balls must be removed.
Let represent the number of red balls removed. Remember that 400 is the number of red balls that were originally in the bag. Setup and solve the proportion:
The number of red balls removed is .
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions