pow 13 phone flub
Alondra forgot Melissa's phone number. She did remember that the first three digits were 357- and that all the rest of the digits in the phone number were 2's and 9's and 7's. Alondra is determined to get in touch with Melissa. I'll just dial phone numbers that fit this description until I reach her. There can't be THAT many, can there? If she is very unlucky, how many wrong numbers might she dial?
if she dials 357-xxxx then there are 3 choices for each "x".
So, there are 3^4 = 81 different numbers consisting of the digits 2,9,7 and only one of them is right.