Handicapping Question

[dean smith]

I understand the practice is often frowned upon in handicapping circles, but when -- if ever -- is betting two horses to win in the same race a good idea? If one of you "math guys" could break it down for me, I'd really appreciate it.

Every great once in awhile, I'll come across a race where I think the top choice(s) are very beatable and I find my top choices to win are going to post with (for instance) 8-1 and 10-1 odds.

I understand by putting ten bucks on each that I'm really now betting 4-1 and 5-1, but if I feel strongly about each having a legitimate shot to win, wouldn't everyone take 4 or 5-1 on their top choice?

Or, is their a better way to approach this situation? In other words, does anyone know the "textbook" way to play this? How would that hypothetical $20 be better used?