Answer:
9000
Step-by-step explanation:
There are 4 numbers (any number from 0-9) in a 4-digit number and the starting number should be 1 or bigger than 1. The thousands place in a 4-digit number cannot be 0. The smallest 4 digit number is 1000 and the greatest 4 digit number is 9999. There are 9000 four-digit numbers in all
