"2 x $30,000 sales sitting at a probability of 10% to close, 1 x $500 sale sitting at a probability of 75% to close", and so on. How does one estimate these pro

"2 x $30,000 sales sitting at a probability of 10% to close, 1 x $500 sale sitting at a probability of 75% to close", and so on. How does one estimate these probabilities?