Question

The sum of all digits in the numbers 44, 45 and 46 is 27 because (4+4)+(4+5)+(4+6)=27. Find the sum of digits in the first 25 counting numbers: 1, 2, 3, …, 25.

Answer 1

The sum is 127

Explanation:

The first 9 numbers have just one digit, so we have:

1+2+3+4+5+6+7+8+9 = 45

Then, for the numbers from 10 to 19, we have:

1+2+3+4+5+6+7+8+9+10 = 45 + 10 = 55

Finally, for the numbers from 20 to 25, we have:

2+3+4+5+6+7 = 27

So the total sum of digits is:

45 + 55 + 27 = 127