Question about implied odds

Hi!

I'm just reading SSH and I love it because it helps me understand why I do things instead of telling me to memorize behavioural patterns in certain situations. But I have a question concerning the implied odds example on p32 though.

I get that the opponent will pay one extra bet with a weak hand (he'll just call my bet). I also get that he will loose 2-5 bets with a strong hand (although in most online poker-rooms there are only 4 bets allowed).
The thing I don't get is: why do I then "guess" that I will have "on average" about 1.5 bets?
Is that a rough estimate or is there any maths behind it that I just fail to see at this moment? I'm feeling a little lost there.

I appreciate any help there.

It's an estimate. Approximately half of the time your opponent will pay only a single bet, and the other half of the time he'll pay approximately two bets. 1+2=3/2 = 1.5 bets.