###### Example2.3.3

If a number plus \(2\) is \(6\text{,}\) what is the number?

One way to solve this riddle is to use the opposite operation. If a number *plus* \(2\) is \(6\text{,}\) we should be able to *subtract* \(2\) from \(6\) and get that unknown number. So the unknown number is \(6-2=4\text{.}\)