You won't dutch 6 or 7 runners and make a profit, dutching is only useful if the runners you are looking at are similar in price, say a runner at $3 then a couple at $5 or $6 if there is a huge difference in price then you are undervaluing the higher priced runners.
The truth is when dutching you are going to hit those $10 and $20 winners and all you will have on them is 10% or so stake.

When backing multiple runners unless you can show a level stakes profit on each selection at that price point compared to the S/R at that price point you are better off not backing that selection.

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