The sum of three different single-digit numbers A, B, C is equal to A + B + C = 20. What can be the smallest value of B?

The specified amount consists of 3 digits and is equal to 20 (A + B + C = 20).
It is necessary to find the smallest digit B that satisfies the condition.

It is clear that the larger the numbers A and C, the smaller the number B. Due to the fact that their sum is unchanged and the larger part will fall on the numbers A and C, the smaller part of this sum will remain on the number B.
So let’s set the digits A and C to the largest possible values – these are digits 9 and 8.

Substitute the found values instead of the numbers A and C:
A + B + C = 20;
8 + B + 9 = 20;
B + 17 = 20;
B = 20 – 17;
B = 3.

Answer: 3.