Probatool

2/10 means 20%?

Actually, far more than that.

The POS lies between 12.77% - 28.85% with confidence: 50%
The POS lies between 9.65% - 34.11% with confidence: 70%
The POS lies between 5.6% - 43.44% with confidence: 90%
Where POS stands for probability of success.

It is the best probability estimating tool ever and easy to use. You only need to enter two numbers and press RUN.

Drag the cursor in the distribution chart to change the interval, the confidence will change correspondingly.

Drag the cursor in the level-confidence chart to change the confidence, the probability cursor will move accordingly, that is the most charming part of this app. You can just assign a dramatically high confidence like 99.99% to get an interval which the POS almost surely lies in.

Probatool uses a mathematical tool called likelihood function to estimate the probability of success based on the number of trials and successes. Unlike the simplest way where POS = Successes / Trials, the statement generated by Probatool contains no uncertainties, because likelihood function is a model of uncertainties.