I think these kind of dutch formulas are pretty generic as far as dutching goes. The important part of dutching with these formulas is that you need to know which runners to omit from the selection. Most of the time the book % for backing is > 100 so the main problem I have is that you cant use this if you dont have some knowledge about the market you're looking at.

Example - 4 horse race (Book percentage = 105%)
Horse 1 = $2 (50%)
Horse 2 = $4 (25%)
Horse 3 = $5 (20%)
Horse 4 = $10 (10%)

Quite feasible. Now using the first method:
P = 105
M = (105/(100-105))+1
= -20

Therefore amount to bet:
H1 = 50 * -20 = -2.5
H2 = 25 * -20 = -1.25
H3 = 20 * -20 = -1
H4 = 10 * -20 = -0.5

So that doesnt work. Right away you need to eliminate a runner...or if you could lay at all those 4 prices you'd be laughing but generally you cant get a lay book percentage > 100.


Second Method
p =105
M =0.9524

Amount to bet:
H1 = 50 *0.9524 = 47.62
H2 = 25 *0.9524 = 23.81
H3 = 20 *0.9524 = 19.05
H4 = 10 *0.9524 = 9.52

Total outlay = $100
BUT no matter who wins the return is only ~ $95.24 (thus meaning a guaranteed loss of $5 for the market)

So my point is that yes these formulas do work but only when you combine with a method to eliminate several runners from the calculations.

If it was a 12 horse race and the book percentage was 105-110 you could easily have to eliminate 5 or so runners to get it under 100 (so that these formulas are useful). Because a runner of 100/1 only reduces the book % down by 1. So you could be dutching only half a race to make a couple of bucks but if any of the missing runners win then you're out the full $100.