Tricky Puzzle!! Please help.

Question

I stumbled upon a puzzle I can't crack. It goes like this:

In a certain Code language:

7321=6

5342=3

8645=15

Then 9312=?

The Answer is 9. But I can't seem to find the logic behind it??

Answer 1

Cool Puzzle! Here is the pattern I found:

$7321:$ Take $7 \cdot 3 \cdot 2 \cdot 1 = 42$. Then $4+2 = 6$.

$5432:$ Take $5 \cdot 4 \cdot 3 \cdot 2 = 120$. Then $1+2+0 = 3$.

$8645:$ Take $8 \cdot 6 \cdot 4 \cdot 5 = 960$. Then $9+6+0 = 15$.

Et Cetera... :-)