In how many whole numbers between 100 and 999 is the middle digit equal to the sum of the other two digits?

Answer 1

45

Here's why:
If first digit is k, middle is k+i, last is i.

Max k+i is 9, so i ranges from 0 to 9-k

So, there are
9 numbers starting with 1,
8 starting with 2,
...
1 starting with 9

sum of numbers from 1 to 9 is 9*10/2 = 45

Answer 2

45

Answer 3

I LOVE MATHS 5+5=10

Answer 4

45

Answer 5

How many whole numbers between 100 and 999 have their digits in strictly decreasing order

Answer 6

198

Answer 7

53. Easy.

Answer 8

ZXedv3c1 niol8

Answer 9

45 btw do u like Olivia Rodrigo?