Poor Dolly’s T.V. has only 4 channels, all of them quite boring. Hence it is not surprising that she desires to switch (change) channel after every one minute. Then find the number of ways in which she can change the channels so the she is back to her original channel for the first time after 4 min.

A student opens a checking account when she starts a new job so that her paychecks can be directly deposited into the account. Her balance can be computed using the expression 10nw+50m where n is the number of hours she works every week and w is the number of weeks that she has worked so far. Assuming she does not withdraw any money from her account, which of the terms in the expressin most logically will change if the student geets a raise ?