3. IN YOUR OWN WORDSHow can you write and evaluate an expression that represents a real-life problem? Give one example with addition, one with subtraction, one with multiplication, and one with division.
A 25.k+10 =25 +10=35 Add 25 and 10.b. Evaluate 4 ⋅nwhen n=12.4⋅n=4⋅12=48 Multiply 4 and 12.1. Evaluate 24 +cwhen c=9. 2. Evaluate d−17 when d=30.EXAMPLEEvaluating Algebraic Expressions1Substitute 25 for k.Substitute 12 for n.Evaluate a÷bwhen a=27 and b=3.a÷b=27 ÷3 =9 Divide 27 by 3.Evaluate the expression when p=24 and q=8.3. p÷q4. q+p5. p−q6. pqEXAMPLEEvaluating an Expression with Two Variables2Substitute 27 for a.Substitute 3 for b.Exercises 8 –19Lesson Tutorials
T-4GoalToday’s lesson is evaluating algebraic expressions.Extra Example 1a.Evaluate 15 −ywhen y =3. 12b. Evaluate 24 ÷w when w =4.6IntroductionConnect• Yesterday:Students explored how to write and evaluate an expression written in words, focusing on units.• Today:The lesson explains how to evaluate an algebraic expression containing a variable.Motivate• Whole Class Activity:Ask five students to stand at the front of the room. Give each student an index card with a number written on the card (possible numbers: 1, 3, 4, 5, 8). Write simple expressions on the board, drawing a box where the variable would be. Students should walk in front of the expression, place their index card in the box, and announce the value of the expression for their number. Examples:+14 27 −2• You can vary the expressions and numbers to fit the level of your class. The goal is for students to recognize that the value changes (or varies) for each number substituted.After several examples, have the students sit down. Erase the boxes and write variables to replace them. “What do the letters mean? Does anyone know what the expressions are called?” The variables have the same meaning as the boxes (an unknown value that represents a number). The expressions are called algebraic expressions.Words of Wisdom• Students can be intimidated by the phrases “numerical expression” and “algebraic expression.” Reassure students that they have been working with each of these types of expressions since they began studying math.