Chapter 5 - Solving for the unknown: a how-to approach for solving equations. After you have mastered the material in this chapter, you will be able to: Explain the basic procedures used to solve equations for the unknown; list the five rules and the mechanical steps used to solve for the unknown in seven situations; know how to check the answers; list the steps for solving word problems; complete blueprint aids to solve word problems; check the solutions.
Chapter 5 Solving for the Unknown: A Howto Approach for Solving Equations McGrawHill/Irwin ©2011 The McGrawHill Companies, All Rights Reserved #5 Solving for the Unknown: A howto Approach for Solving Equations Learning Unit Objectives LU5.1 Solving Equations for the Unknown Explain the basic procedures used to solve equations for the unknown List the five rules and the mechanical steps used to solve for the unknown in seven situations; know how to check the answers 52 #5 Solving for the Unknown: A howto Approach for Solving Equations Learning Unit Objectives LU5.2 Solving Word Problems for the Unknown List the steps for solving word problems Complete blueprint aids to solve word problems; check the solutions 53 Terminology Expression – A meaningful combination of numbers and letters called terms Equation – A mathematical statement with an equal sign showing that a mathematical expression on the left equals the mathematical expression on the right Formula – An equation that expresses in symbols a general fact, rule, or principle. 54 Variables and constants are terms of mathematical expressions Solving Equations for the Unknown Equality in equations A + 8 Left side of equation 58 Right side of equation Dick’s age in 8 years will equal 58 55 Variables and Constants Rules 1. If no number is in front of a letter, it is a 1: B = 1B; C = 1C 2. If no sign is in front of a letter or number, it is a +: C = +C; 4 = +4 56 Solving for the Unknown Rule Whatever you do to one side of an equation, you must do to the other side 57 Opposite Process Rule If an equation indicates a process such as addition, subtraction, multiplication, or division, solve for the unknown or variable by using the opposite process 58 Opposite Process Rule A + 8 = 58 8 8 A = 50 Check 50 + 8 = 58 59 Equation Equality Rule You can add the same quantity or number to both sides of the equation and subtract the same quantity or number from both sides of the equation without affecting the equality of the equation. You can also divide or multiply both sides of the equation by the same quantity or number (except 0) without affecting the equality of the equation 510 Equation Equality Rule 7G = 35 7G = 35 7 7 G = 5 Check 7(5) = 35 511 Multiple Processes Rule When solving for an unknown that involves more than one process, do the addition and subtraction before the multiplication and division 512 Multiple Process Rule H + 2 = 5 4 H + 2 = 5 4 2 2 H = 3 4 Check 12 + 2 = 5 4 3 + 2= 5 513 () (4) H = 4(3) 4 H = 12 Parentheses Rule When equations contain parentheses (which indicates grouping together, you solve for the unknown by first multiplying each item inside the parentheses by the number or letter just outside the parentheses. Then you continue to solve for the unknown with the opposite process used in the equation. Do the addition and subtractions first; then the multiplication and division 514 Parentheses Rule 5(P 4) = 20 5P – 20 = 20 +20 +20 5P = 40 Check 5(84) = 20 5(4) = 20 20 = 20 515 5P = 40 5 5 P =8 Like Unknown Rule To solve equations with like unknowns, you first combine the unknowns and then solve with the opposite process used in the equation 516 Like Unknown Rule 4A + A = 20 5A = 20 5A = 20 5 5 Check 4(4) +4 = 20 16 + 4 = 20 517 A = 4 Solving Word Problems for Unknowns 1) Read the entire Problem 3) Let a variable represent the unknown Y = Computers Read again if necessary 2) Ask: “What is the problem looking for?” 4) Visualize the relationship between the unknowns and variables. Then set up an equation to solve for unknown(s) 4Y + Y = 600 5) Check your results to ensure accuracy 518 Solving Word Problems for the Unknown Blueprint aid Unknown(s) 519 Variable(s) Relationship Solving Word Problems for the Unknown ICM Company sold 4 times as many computers as Ring Company. The difference in their sales is 27. How many computers of each company were sold? Unknown(s) Variable(s) Relationship Cars Sold ICM 4C 4C Ring C C 27 4C C = 27 3C = 27 3 3 C = 9 520 Ring = 9 computers ICM = 4(9) = 36 Computers Check 36 9 = 27 ... multiplication and division 5 14 Parentheses Rule 5( P 4) = 20 5P – 20 = 20 +20 +20 5P = 40 Check 5( 84) = 20 5( 4) = 20 20 = 20 5 15 5P = 40 5 5 P =8 Like Unknown Rule To solve equations ... (except 0) without affecting the equality of the equation 5 10 Equation Equality Rule 7G = 35 7G = 35 7 7 G = 5 Check 7 (5) = 35 511 Multiple Processes Rule When solving for an unknown that ... multiplication and division 5 12 Multiple Process Rule H + 2 = 5 4 H + 2 = 5 4 2 2 H = 3 4 Check 12 + 2 = 5 4 3 + 2= 5 513 () (4)