Thanks Bhagwan, yes that's it in a nutshell.

The maths for laying to a fixed stake are quite simple really. Say we're interested in "Dutching" these horses to lose using a fixed stake of $50.

HORSE A: $ 3.00
HORSE B: $ 6.00
HORSE C: $15.00

For each horse divide 100 by it's price to get the win probablility implied by its odds.

HORSE A: 100/3 = 33.33%
HORSE B: 100/6 = 16.67%
HORSE C: 100/15 = 6.67%

Add the probabilities together to get our book value.

33.33% + 16.67% + 6.67% = 56.67%

Divide the win probability of each horse by the book value.

HORSE A: 33.33/56.67 = 0.5881
HORSE B: 16.67/56.67 = 0.2941
HORSE C: 6.67/56.67 = 0.1176

To determine the stake that should be placed on each horse, we multiply the figure above by the total stake of $50.

HORSE A: 0.5881 * 50 = $29.41
HORSE B: 0.2941 * 50 = $14.71
HORSE C: 0.1176 * 50 = $ 5.88

If HORSE A wins we lose (2*29.41)-14.71-5.88 = $38.23
If HORSE B wins we lose (5*14.71)-29.41-5.88 = $38.26
If HORSE C wins we lose (14*5.88)-29.41-14.71 = $38.20

If none of the three win, we win our stake of $50.

__________________
Pixie

"It's worth remembering that profit isn't profit until it's spent off the racecourse." -- Crash