Expected Count
Part of the Expressions & Data section of Coddy's Pre-Algebra journey. Lesson 36 of 52.
Flip a coin 50 times. How many heads should you expect? The chance of heads is 1/2, and half of 50 is 25: (1/2) × 50 is 25. The expected count is the probability times the number of tries.
Why multiply? A chance of 1/2 says that, in the long run, heads comes up once in every 2 flips, and 50 flips hold 25 such pairs. In the same way, a spinner with a 1/4 chance of blue, spun 40 times, is expected to show blue (1/4) × 40 times, which is 10.
Expected does not mean guaranteed. You might get 23 heads or 28. The expected count is what the results settle around when the experiment is repeated many times, which makes it a good guess, not a promise.
Challenge
A fair die is rolled 120 times. How many sixes c should you expect? Write c equal to the chance of a six times the number of rolls, then work it out.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Expressions & Data
1Variables and Expressions
What a Variable IsWriting ExpressionsExpressions from StoriesTwo OperationsRecap: Expressions2Evaluating Expressions
Substituting a ValueNegative InputsPowers in ExpressionsFormulasRecap: Evaluating5Patterns and Sequences
Continuing a PatternThe Common DifferenceThe nth TermWriting the RuleRecap: Sequences3The Distributive Property
Number PropertiesMental MathDistributing LettersDistributing a MinusRecap: Distributing