# Mensa IQ app: four boxes with four numbers each

Stuck trying to solve this question that popped up the other day. Spent the whole of the 15 minute test trying to find an answer to it.

$$2$$

because

in each box, label the numbers like this:

A B
C D

Then $$B * C = 10A + D$$.

i.e. $$3 * 6 = 18$$, $$7 * 8 = 56$$, and $$9 * 3 = 27$$. So in the final box, we need a $$2$$ to complete the equation $$5 * 4 = 20$$.

I hate this kind of puzzles, since the solution always feels kind of arbitrary to me. Just for the sake of it I suggest an alternative solution:

1

Reason:

The four boxes form a table with four rows and four columns. In each column, label the numbers like this: A B C D Then (A+B+C+D) mod 3 = 0

Now that I think about it, using the same argument, even

7

would be a solution. Depending on your creativity, it appears to me that any given number might be a solution to this problem.