The smallest two-digit number that is not the sum of three different one-digit numbers isA. 10B. 15C. 23D. 25E. 28

To solve this problem, we need to understand that any two-digit number can be the sum of three different one-digit numbers.

Step 1: Start with the smallest two-digit number, which is 10.

Step 2: Check if it can be the sum of three different one-digit numbers. The smallest three different one-digit numbers are 1, 2, and 3. Their sum is 6, which is less than 10. So, 10 can be the sum of three different one-digit numbers.

Step 3: Move to the next smallest two-digit number, which is 11. Repeat the process. The sum of 1, 2, and 3 is still less than 11. So, 11 can also be the sum of three different one-digit numbers.

Step 4: Continue this process until you find a two-digit number that cannot be the sum of three different one-digit numbers.

Step 5: After checking, you will find that the smallest two-digit number that cannot be the sum of three different one-digit numbers is 15.

So, the answer is B. 15.