On Sundays, Bernie's Bagel shop gets very busy. Two hours after they opened, Bernie's sold one third of their bagels. During the next hour, they sold another 50 bagels. During the rest of the day, half of the remaining bagels were bought. At closing, there were only 25 bagels left.

A. How many bagles were left at closing?

B. What operation undoes dividing the number of bagels in half?

C. What operation undoes subtracting 50?

D. How many bagels were in the store when it opened on Sunday?

Work backward ; start with the ending amount of 25 bagels. Then follow the steps you yourself have outlined ; reverse dividing by 2 (what's the opposite of dividing?), then reverse subtracting 50 (what's the opposite of subtracting?). The amount you're now left with will be 2/3 of the original amount, so reverse the 2/3 and you've got it.