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For more information, please see full course syllabus of Pre Algebra
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Lecture Comments (7)

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Post by Henry Sith on August 14, 2013

I was wondering about the reasoning behind the structure of the equations derived from word problems like from the "Extra example 3: Length of the phone call"

Why does it become "0.35 + 0.005m = 1.20" as opposed to "0.05m = 1.20 - 0.35"

Is it solely for the reason that you want to solve the equation by using the inverse operations?

or is the only logical way to write out such an equation so that it makes mathematical sense?, using the mathematical principles?

Sorry if I am wasting your time, I am just a bit cloudy on this.


Thanks

3 answers

Last reply by: Professor Fung
Thu Aug 1, 2013 3:54 AM

Post by Han Jun Kim on July 10, 2013

Could you slow down a bit...it feels like i cant keep up with your writing that fast...but other than that this is a wonderful video

1 answer

Last reply by: Bryan Watts
Sun Apr 21, 2013 9:41 PM

Post by Kumar Sandrasegaran on May 17, 2011

Question solving two-step equation is a bit hard to understand. You see, I'm not doing really any
biology at school. You mention how iron is related to vitamin c but never say anything about zinc. Next time please inform all students they must take a mini biology course before watching this video. Nicole

Solving Two-Step Equations

  • A two-step equation has two operations. You will need to cancel or undo each one by using its inverse operation.
  • Addition and subtraction are inverse operations. You can use the Addition Property of Equality and the Subtraction Property of Equality to undo the opposite operation.
  • Multiplication and division are inverse operations. You can use the Multiplication Property of Equality and the Division Property of Equality to undo the opposite operation.
  • Remember to work backwards from the order of operations. Undo addition and subtraction first, then multiplication and division.

Solving Two-Step Equations

4x − 3 = 81
  • 4x = 81 + 3
  • 4x = 84
  • x = [84/4]
x = 21
45 = [x/3] + 17
  • 45 − 17 = [x/3]
  • 28 = [x/3]
84 = x
11 + 8y = 59
  • 8y = 59 − 11
  • 8y = 48
  • y = [48/8]
y = 6
13x + 4 = 43
  • 13x = 43 − 4
  • 13x = 39
  • 4x = [39/13]
x = 3
− 2m − 63 = 47
  • − 2m = 47 + 63
  • − 2m = 110
  • m = [110/( − 2)]
m = − 55
− 5 = − 19 − [t/7]
  • − 5 + 19 = − [t/9]
  • 14 = − [t/9]
  • 14 ×9 = − t
  • 126 = − t
t = − 126
Duy begins with 16 gallons of gas in his car. His car uses 3 gallons of gas per hour of driving. He will stop to get more gas when there is 1 gallon left in the tank. After how many hours will Duy need to stop to refuel?
  • Let t = how long Duy drives
  • 16 gallons − (3 gallons per hour)t = 1 gallon
  • − 3t = 1 − 16
  • − 3t = − 15
t = 5 hours
A phone plan costs $ 0.45 per call and $ 0.10 per minute. You pay $ 2.30 for the call. Write and solve an equation to find the length of the call.
  • Let m = the length of the call.
  • $ 2.30 = $ 0.45 + $ 0.10m
  • $ 2.30 − $ 0.45 = $ 0.10m
  • $ 1.85 = $ 0.10m
  • m = $ 1.85 ÷$ 0.10
m = 18.5 minutes
You go to a county fair. It costs $ 11 to enter the fair, and it costs $ 3 for each ride at the fair. You spend $ 26 at the fair. How many rides did you ride?
  • Let r = number of rides you rode
  • $ 26 = $ 11 + $ 3r
  • $ 26 − $ 11 = $ 3r
  • $ 15 = $ 3r
  • r = $ 15 ÷$ 3
r = 5 rides
Eric buys one sandwich for $ 5.30 and 5 drinks. The total cost is $ 19.05. How much does one drink cost?
  • Let d = cost of one drink.
  • $ 5.30 + 5d = $ 19.05
  • 5d = $ 19.05 − $ 5.30
  • 5d = $ 13.75
  • d = $ 13.75 ÷5
d = $ 2.75

*These practice questions are only helpful when you work on them offline on a piece of paper and then use the solution steps function to check your answer.

Answer

Solving Two-Step Equations

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • What You'll Learn and Why 0:06
    • Topics Overview
  • Two-Step Equation Involvement 0:19
  • Solving Two-Step Equations 0:41
    • Example: 8y - 11 = 32
    • Example: 32 = t/5 + 8
  • Solving Two-Step Equations 4:49
    • Example: Recommended Daily Intake
  • Solving Two-Step Equations 7:01
    • Example: Cost of Each Ride
  • Extra Example 1: Solving Two-Step Equations 10:13
  • Extra Example 2: Solving Two-Step Equations 12:54
  • Extra Example 3: Length of Phone Call 13:56
  • Extra Example 4: Cost of Owning a Pet 16:40