Question
In how many whole numbers between 100 and 999 is the middle digit equal to the sum of the other two digits?
Answers
Steve
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
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
Anonymous
45
ALEX
I LOVE MATHS 5+5=10
Alice
45
Ransa
How many whole numbers between 100 and 999 have their digits in strictly decreasing order
Nick
198
anon.
53. Easy.
Reeet
ZXedv3c1 niol8
Oscar
45 btw do u like Olivia Rodrigo?