Problema Solution
Debbie forgot Linda's phone number. She did remember that the first three numbers were 297- and that all the rest of the digits in the phone number were 2s 9s and 7s. If she was very unlucky, how many wrong numbers might she dial?
Answer provided by our tutors
There are 4 digits left:
There are 3 choices for each digit....
So 297- (First digit left) 3 choices
Times
(Second Digit Left) 3 choices
Times
(third Digit Left) 3 choices
Times
(Fourth Digit Left) 3 Choices
3^4-1
81-1 80