this ones hard, i think. i cant find a patten. I asked my step dad whos a wiz at maths and he cant get it either. So anyone who can help please do. Thanks

if 5 * 3 = 4

2 * 8 = 2

6 * 3 = 3

find the value of

1 * 7

One more thing a patten i cant get -

2 1/2, 5 , 10 , 20 _ _

Thanx for all your help Dan it was awesome!! Saved me thank -you heapss xo