1 2 3 4 5 6 7 9
Take the paper from him and, after pretending to scrutinise the row, ask
him to point out which figure he considers most imperfectly made. If he
should select the 1, say, "You had better practise making that figure.
Oblige me by multiplying the row by nine." When he does so the result
will be
1 1 1 1 1 1 1 1 1
Then say, "After this practice you will be able to make better ones in
future."