Suppose a building has 10 floors. m people get into the elevator at level 0 and each one independently and uniformly at random chooses a floor between 1 and 10. what is the expected number of stops of the elevator?

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?