Question

Using the digits 1 through 8, how many unique 2-digit numbers can be made?

Answer 1

56

Explanation:

In the tens position we can put one of eight numbers. The same is true for the ones position. And so we take 8 possibilities in the tens and multiply by 8 possibilities in the ones:

`8xx8=64`

Now - this will include duplicates. If one of our numbers is `88`, we can make `8_1 8_2` and `8_2 8_1`. How many duplicates are there? Eight (one each for each possible digit). And so:

`64-8=56`