
In the last sentence:
"A winning punter will win $4 for each $5 bet. Assuming that the punters will win 50% of the time, the bookmaker only has to pay out on average $80 for each $100 gambled, yielding a profit margin of 20%."
Punters winning 50% of the time implies that out of the $100 dollars gambled $50 will be winning bets. The bookie gets $100 upfront, but has to pay out $50 (winning bets) + $40 (winning gains), leaving him $10, which is a 10% gain on $100.
I'm not sure how the $80 payout is calculated, would you please clarify?
Thanks in advance, (and for a great book!)
