Alice bought a number of ping pong balls in a store where a 5% sales tax is added to every purchase. If she did not have to pay tax, she could have bought three more balls for the same amount of money. How many balls did she buy?

Due to a packaging error, 4 cans labeled diet soda were accidentally filled with regular soda and placed in a 12 pack carton of diet soda. two cans were randomly selected from this 12 pack. what is the probability that both cans were regular soda?