While doing a problem on his calculator, Tom meant to divide a number by 2

While doing a problem on his calculator, Tom meant to divide a number by 2, but instead he accidentally multiplied the number by 2. Which of the following calculations could Tom then do to the result on the calculator screen to obtain the result he originally wanted?

1. Subtract the original number
2. Multiply by 2
3. Multiply by 4
4. Divide by 2
5. Divide by 4

Answer

The correct answer is E.

You can assume an even integer as Tom’s initial number, follow his steps in obtaining the incorrect answer, and then determine what operation using what number is needed to obtain the desired number. For example: 

Choose the integer 6 as the initial number. When Tom "accidentally multiplies the number by 2," he obtains an incorrect answer of 12. Had Tom correctly divided the initial number by 2, he would have obtained 3 as the answer.

To convert his incorrect answer of 12 to the desired answer of 3, he must divide by 4.