If Katherine has 4 apples and 3 times as many pears in her fridge, how many bananas does she have if she has a total of 21 pieces of fruit? Think carefully first, then make a decision:
Katherine has a total of 3 * 4 apples = 12 pears. She therefore had 4 apples + 12 pears = 16 apples and pears. We know she has 21 total pieces of fruit, so this means she must have 21 total - 16 = 5 bananas. So, the answer is 5.