I hated school and was terrible at maths so be gentle with me; I hear this angle now and again and have never understood how on earth betting a single each way at 2/1 even at quarter the odds can ever be a profitable bet??
Ok. First thing you're looking for is whether the place market is overround or overbroke (assume you're familiar with this)?
Imagine 8 runners, 1/5 the odds a place.
Your 2/1 shot, decimal odds 3. You're getting 2/5 to place, decimal odds 1.4. This implies a 71.4pc chance of placing (1 divided by 1.4 is 0.714)
Do this for all the runners and add them together. As there are three places the real life probability of all the horses placing added together should be 300pc.
If the number you get is less than 300pc this means the place market is overbroke and the odds are in your favour. The profit margin built into a market by a bookmaker has is now in your favour. The maths more often than not work out when there is a shortish priced favourite.
Let's use a realistic example market, including your 2/1 shot.
4/5
2/1
5/1
20/1
25/1
40/1
50/1
66/1
The win chances add up to 120pc - nothing out of the ordinary here, the bookie has a 20pc margin in their favour.
But the place chances add up to 272pc - i.e. Overbroke. Of course you can't just take the place part of the bet, but if you could, you could theoretically stake £272 for a guaranteed £300 return. This is what's meant by bad ew. Bets in these markets combined into multiples can be powerful compounders of value, and will often lead to account closure.
Returning to your 2/1 shot, on which you're getting 1.4 to place. Look at the betfair place market and you'd see that it's more like 1.25 to place - which shows you're getting ew value, provided you're happy with the win side of the bet.
Sorry if that's a bit long winded. I'll happily send you my spreadsheet I made for working out quickly whether a race is bad ew.
