Re: quickly calculating odds.
This is called the 2x and 4 x rule .
That is , when you have 2 cards to come with x outs , then the percentage of time your hand hits is about 4x% . When you have one card to come , then the percentage of time your hand hits is 2x% .
With one card and x outs , the probability is x/47=~x/50=2x/100 . This is how we get 2x % .
With 2 cards to come , the probability is x/47 + x/47 - xc2/47c2 =~ x/47+x/47 =~ x/50+x/50 =~2x/100+2x/100=~4x/100 or 4x % .
Notice that I disregarded the negative term xc2/47c2 since this will be about 0 .
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