Hi Cairns punter,
That $10 is the allocated base amount for each horse.
You can make this to be 1/40th of your bank.

There is a built in Dutching calculator than do this same exercise for you in the Bet Trader Pro program that I mentioned before, they call it the Bookie program.
You simply place say $10 in the top box then enter your accessed odds into the horses cell next to it, then submit each one individually as their prices come to be greater than your assessed price.
Its all worked out for you.
It works a treat for this exercise.

__________________
Cheers.