Here is the way to calculate what your bet will do to the place dividend.

1. Get the starting pool value (in this example $10,000)
2. Multiply this value by .8575 to give the amount that will actually be distributed to the punters. So $10000 * .8575 = $8575
3. Divide this by 3 (assuming 3 places paid) to give the amount to be distributed for each placing. So $8575 / 3 = $2858
4. Divide this amount by the current price to see roughly how much is invested on the runner at the moment. So $2858 / 1.50 = $1905

Now we need to work out what it will be after your $500 bet.

1. New pool value will be $10,500
2. Amount to be distributed = $9003 (10500 * .8575)
3. Amount per placing = $3001
4. The amount invested on your runner (so the old value plus your $500) = $1905 + $500 = $2405
5. New dividend is amount available per placing divided by the amount on your runner. So $3001/$2405 = $1.25 (which, of course, would be rounded down to $1.20)

So a $500 place bet on a $1.50 runner in a $10,000 pool will reduce the dividend down to $1.20. Of course this assumes nobody else is placing bets and it also depends on what the actual unrounded dividend was (if the original div should be $1.59 but is being rounded to $1.50 then you will only go down to $1.30).

Working out the win pool is the same except you don't have to do the division by 3 bit.

Hope this is what you are after.

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