Question

How many 8-digit numbers are there in all?

Answer 1

There are 10 digits i.e., 0, 1, 2, 3, 4, 5, 6 ,7, 8, 9.
We can not use '0' at the place having the highest place value in 8 digit numbers
So, we can use only 9 digits at the place having the highest place value in 8 digit numbers
Also, we can use 10 digits at the remaining places in 8 digit numbers
So, total numbers of 8-digit numbers = 9 × 10 × 10 × 10 × 10 × 10 × 10 × 10 = 90000000