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Learn to solve multi-step equations easily with the DO-UNDO method. Understand the order of operations and undo steps like dividing by 5 and adding 9 to isolate the variable. Practice with examples and a DO-UNDO chart for quick solutions. Challenge yourself with various equations. Don't forget to check your answers!
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2.4 Solving Multi-Step Equations Indicators: PFA7, PFA8, PFA9 Written by ??? Edited by Eddie Judd, Crestwood Middle School
Ex: x + 9 = 6 5 Ask yourself: What is the first thing we are doing to x? The second thing? Recall the order of operations as you answer these questions. dividing by 5 adding 9 To undo these steps, do the opposite operations in opposite order. To Solve: Undo the operations by working backward.
Use a chart as a shortcut to answering the questions. DO UNDO ÷5 -9 +9 ·5 Follow the steps in the ‘undo’ column to isolate the variable. Ex: x + 9 = 6 5 First subtract 9. x + 9 - 9 = 6 - 9 5 x = -3 5 Then multiply by 5. (5) x = -3(5) 5 x = -15 The DO-UNDO chart
Complete the do-undo chart. DO UNDO -2 ·3 ÷ 3 +2 To solve for d: First multiply by 3. Then add 2. Ex: d - 2 = 7 3 (3) d - 2 = 7(3) 3 d - 2 = 21 d - 2 = 21 +2 +2 d = 23 Let’s try another!
Remember to always use the sign in front of the number. DO UNDO ÷ -7 - 3 +3 · -7 To solve for a: First subtract 3. Then multiply by -7. Ex: 3 - a = -2 7 3 - a = -2 7 -3 -3 - a = -5 7 (-7)(- a) = (-5)(-7) 7 a = 35 Here’s a tricky one!
Try a few on your own. • 5z + 16 = 51 • 14n - 8 = 34 • 4b + 8 = 10 -2
DO UNDO · 5 - 16 +16 ÷ 5 z = 7 DO UNDO · 14 +8 -8 ÷ 14 n = 3 The answers: • DO UNDO • · 4 · -2 • +8 - 8 • ÷ -2 ÷ 4 • b = -7
Assignment • Page 95 Problems 9-31 all and 33-37 odds • Regular Algebra 1 • Page 95 Problems 11-23 odds, 25-28 all, and 31,36,37,40-42 • Honors Algebra 1