Question

number machines
challenge #3
quinn put a number into the machine, and 15 was the output.
what was the input?
(the machine has two operations: add 13 and divide by 2)

Explanation:

Step1: Reverse the operations. First, reverse the "Divide by 2" operation.

If the output after dividing by 2 is 15, then before dividing by 2, the number was $15\times2 = 30$.

Step2: Reverse the "Add 13" operation.

Now, reverse the "Add 13" operation. If after adding 13 we got 30, then the original input was $30 - 13 = 17$.

Answer:

17