Question

What is the sum of all possible digits that could fill in the blank
in 47_021 so that the resulting five digit number is divisible by 3?

Answer 1

I have news for you. If I add a number to the blank, it makes six digits. My eyes are old and bad but not that bad (but still that old).

Answer 2

DrBob is right, you have a typo.

Nevertheless there is a nice quick way to check if any number is divisible by 3

Add up all the digits in the number, if that sum is divisible by 3 so was the original number.

so far the digits of 47_021 add up to 14, so you could add 1,4 or 7 and in each case the new number would be divisible by 3