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Betfair Historical data files, comes only with back prices. For me it's ok with markets of 2 selections,ex:

Market Under/Over 2.5 Given Under Back Price 1.73 ---> Under Lay Price ??? Over Back Price 2.26

I can calculate "Under Lay Price" inverting the "Over Back Price 2.26"

(1/2.26)*100 = 44.25% ---> 100% - 44.25% = 55.75% ---> 100/55.75 = 1.79 Done

But when more than 3 selections I can't calculate so far. Ex:

Only Back Prices given from Betfair Historical data files

Home 2.20 Away 3.50 Draw 3.30 or Home 45.46% Away 28.57% Draw 30.30%

Now how to calculate the Lay prices based on the back prices?

Thanks in advance!

PS: The result Lay Prices I know they must be Home 2.38, Away 3.9 and Draw 3.6.

jer
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  • Have you tried anything so far ? – Mustapha Belmokhtar Jan 13 '19 at 01:50
  • Yeah, on 3 selections, I think the lay is done by other 2 backs or direct lay bets that doesn't reflect on back odds, ex: find lay odd of Draw (must be, 3.6 or 27.78%), I can work out with Home and Away back odds 45.45%(2.2) and 28.57%(3.3). Adding and invert abs(100-(45.45+28.57)) = 25.97% which is a good approximation to 27.78%. Following the same method, Home 41.13% and Away 24.24%. So, being the end result Home Away Draw effective “42.02% ; 25.64% ; 27 .78%”, not bad approximation of “41.13% ; 24.24% ; 25.97%” Didn't work @ 9 selections. So I guess must be something else!!! – jer Jan 13 '19 at 11:59

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