[mute]

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for first thanks to all and please excuse me for bad english language....
Wolfram :thanks to you ,I now understand that "When you're at the river, you don't take the action on previous streets into account to calculate expected value"

example:

at river i call with higmidpair a single bet(1$) for 1000
times,
my total spent is 1000$

in this 1000 times i win 300 pot ,the sum of this 300 pot-win is 1200$
my total win is 1200$

formula:
monet spent for river call=RC
sum of pot win=PW
total is=PW-RC 200$

ok?
i think this is correct,you can confim ?

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Not quite right since you don't "spend" 1000$ by calling the river. You get your money back when you win.

Here's a simpler way:

Potsize is 4 bets. You win 3/10 times and lose 7/10 times.

(3*4) - (7*1)/10 = 0.5 bets

So you win 0.5 bets by calling (or 500$ if you did it 1000 times).

EDIT: What mvoss said.