A factory has three machines, and one faulty bolt is found in the box. Which machine made it? You know how often each machine makes a faulty bolt, and now you want to run the question backwards. Split the world into cases, add the cases with the law of total probability, and reverse a condition with Bayes' theorem. Then meet the traps that catch even careful readers, from screening tests to the game show with three doors. It covers the second part of the Indian syllabus unit (NCERT, JEE Main) and the matching topics of A-Level, IB and AP.
3 lessons, about 1 h 25 min3 simulations10 problems3 practice questionsPython in every lesson
When the world splits into cases that cannot overlap and that cover every possibility, the probability of an event is a sum over the cases. Multiply the chance of each case by the chance of the event in that case, then add. This lesson shows the partition, the law of total probability, the tree diagram that adds the right paths and the usual slips.
Bayes' theorem turns a probability around. You know how likely a result is under each possible cause. The theorem tells you how likely each cause is once you have seen the result. This lesson gives the formula, the words prior, likelihood and posterior, and the method of natural frequencies, with factories, urns and a medical test.
A good test can still give a poor answer. This lesson names the four numbers that describe a test, shows why the rate of an illness matters so much, and meets the traps that catch careful readers: the prosecutor's fallacy, the two-child puzzle, the game with three doors and the updating of a result by a second test.
Log in to join the discussion.
Loading…