If a blacksmith requires five minutes to put on a horseshoe, show how can 8 blacksmiths shoe 10 horses in less than half an hour?

The catch: A horse can stand on three legs, but not on two.

Of course to lessen the changes of horse and blacksmith, it might be better to keep the same blacksmith with the same horse when possible:

a1 b2 c3 d4 e5 f6 g7 j8
b2 c3 d4 e5 f6 a7 h8 i1
c3 d4 e5 b6 g7 h8 i1 j2
d4 c5 f6 g7 h8 i1 j2 a3
e5 f6 g7 h8 i1 j2 a3 b4