math
posted by jake .
how many possible 3 digit numbers are there that have a middle zero? how many possible 4 digit numbers are there that have two middle zeros? Explain your answears

In the first case, you are free to choose only the first and lat digits. The first digit must start with 1 and there are 9 of them. The last digit can start with any number 0 to 9, and there are 10 of them. That makes the number of possibilities 9x10 = 90
Try your own hand at the second one. There are a lot of similarities with the first.