You roll a die behind a screen, and a friend peeks and says the number is even. What is the chance it is a six? The answer is no longer one in six. Learn to shrink the sample space with a condition, to multiply along the branches of a tree diagram, and to decide when two events do not affect each other at all. It covers the first part of the Indian syllabus unit (NCERT, JEE Main) and the matching topics of A-Level, IB and AP.
3 lessons, about 1 h 15 min3 simulations10 problems3 practice questionsPython in every lesson
A probability can change when you learn something new. Once you know that event has happened, the sample space shrinks to , and the probability of becomes . This lesson shows the reduced sample space, the formula, the notation of Indian books and of A-Level, IB and AP, and the usual slips.
Rearrange the conditional probability formula and you get the multiplication rule, . A tree diagram lays out the stages of an experiment: multiply along a path and add across paths. This lesson covers draws with and without replacement, chains of three events and the shortcut for "at least one".
Two events are independent when knowing that one has happened does not change the probability of the other. Then . This lesson tests for independence, separates it from mutually exclusive events, treats three events together and uses the idea for components in series and in parallel.
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