Here's some useful stuff to add to King Yao's formula.
On the flop, if there are X big bets, you need Y number of outs as a break-even to call one bet as the presumed underdog.
2 Big Bets: just better than 9 outs
(Good Number = 2 * 9 * 2 = 36
( Bad Number = 48-9= 39)
3 Big Bets: 7 outs
(Good number = 7 * 3 *2 = 42)
(Bad Number = 48-7 = 41)
4 Big Bets: 5.5 outs
(Good Number = 4 * 5.5 * 2 = 44)
(Bad Number = 48-5.5 = 42.5)
5 Big Bets: 4.5 outs
(Good Number = 5 * 4.5 * 2 = 45)
(Bad Number = 48-4.5= 43.5)
6 Big Bets: 4 outs
(Good Number = 6 * 4 * 2 = 48 )
(Bad Number = 48-4 = 44)
