Hi

I have a question which asks to identify the missing number as follows:

__________

| 7 | 8 |

| 5 | 6 |

|------------

_________

| 20 | 1 |

| 2 | ? |

--------------

possible answers are: 3 or 16 or 25 or 48 or 17.

I didn't draw it but the sets of four numbers above are in square girds - hope that makes sense. The others of this type I could work out fairly easily, it is just this problem. What is the ? and why?

Angus