Question

How many 9 digit numbers have their first and last digits even?

Answer 1

There are 900000000 nine-digits numbers and exactly half of them have an even sum of digits (because every number can be paired with another of the opposite parity by changing the last digit).

Answer 2

Answer:  200,000,000.

we have 9 spaces we need to fill in

There are 10 total numbers(0–9)

There are 5 even numbers(0,2,4,6,8)

fill from left to right

u cannot start with 0 so pick another number 2,4,6,8 any of those

4*10^7*5= 20*10^7 = 2*10^8

200,000,000.