Math CentralQuandaries & Queries


Question from Breanna, a student:

The code is made up of five two digit numbers from 01 to 20 entered in a certain order. How many different security codes are possible with this system

Hi Breanna,

From the way you have described this you can repeat the two digit numbers, for example

15 06 15 15 06

is a valid security code.

Thus for each of the 5 two digit numbers there are 20 possibilities, any number from 01 to 20,

Can you complete the solution from here?


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