Question

To reach a particular department at a warehouse, a caller must dial a 4-digit extension. Suppose a caller remembers that the first and last digits of an extension are 5, but they are not sure about the other digits.

How many possible extensions might they have to try?

Answer 1

100 possible extensions

Explanation:

we can calculated how many possible extensions they have to try using the rule of multiplication as:

___1_____*___10_____*___10_____*____1____ = 100

1st digit 2nd digit 3rd digit 4th digit

You know that the 1st and 4th digits of the extension are 5. it means that you just have 1 option for these places. On the other hand, you don't remember nothing about the 2nd and 3rd digit, it means that there are 10 possibles digits (from 0 to 9) for each digit.

So, There are 100 possibles extensions in which the 5 is the first and last digit.