Henry Ernest Dudeney/Modern Puzzles/88 - Correcting an Error/Solution

by : $88$

 * Correcting an Error

Solution

 * $912$

Proof
Let $x$ be the multiplicand.

Misplacing the partial product as described causes the multiplier to be $49$ and not $409$.

Hence we have:
 * $409 x - 49 x = 328320$

which after some simple algebra gives:
 * $x = 912$

Easy peasy lemon squeezy.