We need to calculate the total of all the individual digits in the numbers ranging from 10 to 100.

•   We will exclude the number 100 for now and focus on the numbers from 10 to 99.

•   This leaves us with 9 groups of 10 numbers each.

•   10, 11, 12, …. 19

•   20, 21, 22, …. 29

•   30, 31, 32, …. 39

•   …

•   …

•   90, 91, 92, …. 99

Counting Units Digits

•   The sum of the unit digits in each of these nine sets = 0 + 1 + 2 + …. + 9 = 9 × 10 / 2 = 45.

•   Note: The sum of the first n natural numbers = n (n + 1) / 2.

•   Therefore, the sum of all the unit digits in the nine sets is 45 × 9 = 405.

Counting Tens Digits

•   First, we count the tens digits of the tens digits of 10, 20, 30 …, 90, and then 11, 21, 31, …, 91, and so on.

•   The sum of the tens digits in numbers from 10 to 90 = 1 + 2 + 3 + …. + 9 = 9 × 10 / 2 = 45.

•   Hence, the sum of all the tens digits is 45 × 10 = 450.

Combining Units and Tens Digits

•   The total sum of digits in numbers from 10 to 100 is:

•   405 (sum of unit digits) + 450 (sum of tens digits) + 1 (for the number 100) = 856.

•   Therefore, option (b) is correct.