What is the sum of all digits which appear in all the integers from 10 to 100?
What is the sum of all digits which appear in all the integers from 10 to 100?
855
856
910
911
Solution
Sum of digits of all integers from 1 to 99 is 900. From 1 to 9 the digit sum is 45, so from 10 to 99 it is $900 - 45 = 855$. Adding 100 contributes digit sum 1, giving $855 + 1 = 856$.