Question

How many three digit numbers are there that have the property that one digit is the sum of the other two digits?

Answer 1

Ways to get an even sum:
22 odd 11 even.
33 even.
First case:
First see that there are three posiblities for the place the even number takes: (the first number cant be 0 because then it would not be a 3 digit number. Therefore there are (4∗5∗5)+2(5∗5∗5)(4∗5∗5)+2(5∗5∗5) ways
second case: all even. there are 4∗5∗54∗5∗5 ways to do it therefore the total is 100+250+100=450100+250+100=450 numbers