Sum-Things Missing Puzzle - Solution

The Puzzle:

Sum-Things Missing
An old Mathematics book contained this addition sum which had been marked correct by the teacher:



The three squares in the diagram are where the paper was so bad I couldn't read them.

What were the three missing numbers?




Our Solution:

The most obvious place to start was the 0 on the bottom (don't forget to carry the 1!).

Working towards the left, the next one has to be 9 to make the total 16 (+1 = 17) so we carry another 1.

That means the top left digit must be empty (or a zero):



Puzzle Author: Stephen Froggatt

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