The Complement
Part of the Expressions & Data section of Coddy's Pre-Algebra journey. Lesson 34 of 52.
Something either happens or it does not, so those two chances add up to 1. If the chance of rain tomorrow is 3/10, the chance of no rain is 1 - 3/10, which is 7/10.
Why subtract from 1? A probability of 1 stands for all the possible outcomes. They split into the ones where the event happens and the ones where it does not, so the second chance is whatever the first leaves over. The event not happening is called the complement.
The complement is quickest when the event itself is awkward to count. The chance of rolling anything except a six is 1 - 1/6, which is 5/6: one subtraction instead of counting five faces.
Challenge
A spinner lands on gold with probability 2/9. Find the probability q that it does not land on gold.
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