Henry Ernest Dudeney/Puzzles and Curious Problems/173 - Short Cuts/Solution

by : $173$

 * Short Cuts

Solution
To multiply $993$ by $879$, proceed as follows:


 * Transfer $7$ from $879$ to $993$, and we get $872$ and $1000$.


 * Multiply these together to make $872 \, 000$.


 * Subtract $872$ from $993$ to get $121$.


 * Multiply $121$ by the $7$ we mentioned above, and get $847$.

Add the two results together, and you get $872 \, 847$.