Flies are Betty's frog's favorite food. Every day the frog eats 2 flies. Betty puts the flies she finds in a bottle. In the morning Betty catches 5 flies inside a bottle, and in the afternoon she catches 6 more, but when she removes the lid, one escapes. Betty wants to gather the whole week's food for her frog. How many more flies does she need? Think carefully first, then make a decision:
The frog eats 2 flies / day * 7 days / week = 14 flies a week. Betty catches flies in the morning and in the afternoon, for a total of 5 flies + 6 flies = 11 flies. But 1 fly escapes, leaving 11 flies - 1 fly = 10 flies. To get her frog's food for the whole week, Betty needs 14 flies - 10 flies = 4 more flies. So, the answer is 4.