Request a friend to write the following figures:—
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 53 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.”
If he selects the 4 request him to multiply by 36 and the result will be
4 4 4 4 4 4 4 4 4
Whichever figure he selects, mentally multiply it by 9 and request him to multiply the row by the result. If he thinks 9 the most imperfectly made figure, you, of course, tell him to multiply by 81 and the result will be all 9’s.
FOUR NINES PROBLEM
How can four 9’s be written so that they will make 100?