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.