Question: Tomorrow, Pete must finish paying off the last $90 he owes on a bike. He goes through his wallet and finds two $20 bills. Checking his pockets, he finds four $10 bills. Unhappy that he doesn't have the entire amount, he suddenly remembers that he has plastic bottles that can be returned to his local store for cash. If the store pays 50 cents for each bottle, how many bottles will Pete have to return to the store? Think carefully first, then make a decision:
Pete's wallet contains 2 * 20 = 40 dollars. The money in Pete's pockets is 4 * 10 = 40 dollars. In total Pete has 40 + 40 = 80 dollars. He owes 90 dollars on the bike and therefore needs 90 - 80 = 10 more dollars. Since 50 cents is dollar, then the number of bottles required to get 10 dollars is 10 / (1 / 2) = 10 * 2 = 20 bottles. So the answer is 20.