Morning Jim
After the results are in you % of 2nds is correct,give or take a % .
The trouble with finding the correct odds at the start is that all the races will have a different amount of horses running in those races...eg More of a chance a horse could get 2nd in a 8 horse race,as opposed to a 16 horse race.
I don't have a correct answer to you question,as i have never been asked or ever seen odds been offered on such a bet before.
The only way i can see such a bet is if the bookies said - There are eg. 5 meetings today 30 races - how many will come 2nd ?
BUT = The bet would look like this - 0-8 (odds) 9-12 (odds) 13 or more...you would have to give your selection over and they would work out the % of those horse - which again i can't see them offering you odds as they will say that :
You can put them selcetions in a place acc - do a placepot ( if 6 are at the same meeting ).
The true odds are for placed ( 2nd and 3rd ) 5 placed horses ALL AT 5-1 and at 1-5 odds = 32-1.