Two Operations
Part of the Expressions & Data section of Coddy's Pre-Algebra journey. Lesson 4 of 52.
"3 less than 10" is 7, which is 10 - 3. The number you start from is the one written last. So "3 less than a number n" is n - 3, not 3 - n. The words "less than" reverse the order in which you read them.
The order matters because swapping the two sides of a subtraction changes the answer: 10 - 3 is 7, but 3 - 10 is -7. With addition it does not matter, which is why "more than" never causes trouble.
Many phrases use two operations. Twice a number means 2 times it, and "three times a number k" is 3k. So "4 more than three times a number k" is 3k + 4, and "8 less than three times a number k" is 3k - 8: build the product first, then add to it or take away from it.
Challenge
Write an expression for "5 less than twice a number n". Type it as a new line on the board, then press Check.
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