For more information, please see full course syllabus of Pre Algebra

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For more information, please see full course syllabus of Pre Algebra

For more information, please see full course syllabus of Pre Algebra

### Estimating for Reasonableness

- Estimation is used when an exact answer is not needed.
- Most estimation techniques involve replacing numbers and with ones that are close and easy to compute mentally.
- Compatible numbers do not always follow the rules of estimating. For example, 310 ÷ 65 by using compatible numbers is 300 ÷ 60 = 5 compared to estimating which would be 300 ÷ 70.

### Estimating for Reasonableness

Estimate 273 ÷ 28 using compatible numbers.

- 273 is close to 270.28 is close to 30.
- 270 ÷ 30 =

9

Estimate 37 × 3 using compatible numbers.

- 37 is close to 40.
- 40 × 3 =

120

Estimate 694.3 - 125.5 to the nearest ones place.

- 694.3 rounds to 694
- 125.5 rounds to 126
- 694 - 126 =

568

Estimate 1,927.5638 + 52,934.56 to the nearest hundreds place.

- 1,927.5638 rounds to 1,930.
- 52,934.56 rounds to 52,930
- 1,930 + 52,930 =

54,860

Estimate 56.783 - 5.477 to the nearest hundredths place.

- 56.783 rounds to 56.78.
- 5.477 rounds to 5.48.
- 56.78 - 5.48 =

51.30

What is 129 × 52 using compatible numbers?

- 129 is close to 130
- 52 is close to 50.
- 130 × 50 =

6500

You go out to eat and order a salad for $ 4.95, soup for $ 3.65, and steak for $ 11.99. What is the estimated total cost of your meal?

- $ 4.95 is close to $ 5
- $ 3.65 is close to $ 3.50
- $ 11.99 is close to $ 12
- $ 5 + $ 3.50 + $ 12 =

$ 20.50

Margaret is saving money to buy a new jacket that costs $ 29.78. She has already saved $ 12.43. Around how much more money does she still need to save buy the jacket?

- The word Around tells us we need to estimate the amount
- $ 29.78 - $ 12.43 = the exact amount of money Margaret still needs
- $ 29.78 rounds to $ 29.75
- $ 12.43 rounds to $ 12.45
- $ 29.75 - $ 12.45 = the estimated amount of money Margaret still needs

$ 17.30

You buy shoes for $ 14.56, socks for $ 3.21, and pants for $ 29.07. The total comes to $ 46.84. Is this reasonable?

- $ 14.56 rounds to $ 14.60
- $ 3.21 rounds to $ 3.20
- $ 29.07 rounds to $ 29.10
- $ 14.60 + $ 3.20 + $ 29.10 =
- $ 46.90, which is indeed close to the total of $ 46.85

Yes

Derrick buys a book for $ 10.92, a backpack for $ 37.89, and a calculator for $ 12.53. The total comes to $ 80.34. Is this reasonable?

- $ 10.92 rounds to $ 11
- $ 37.89 rounds to $ 38
- $ 12.53 rounds to $ 12.50
- $ 11 + $ 38 + $ 12.50 =
- $ 61.50, which is not close to the total of $ 80.34

No

*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

### Estimating for Reasonableness

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
- What You'll Learn and Why
- Vocabulary
- Estimating by Rounding
- Estimating with Compatible Numbers
- Estimating for Reasonableness
- Extra Example 1: Estimating with Compatible Numbers
- Extra Example 2: Estimating by Rounding
- Extra Example 3: Estimating for Reasonableness
- Extra Example 4: Estimating for Reasonableness

- Intro 0:00
- What You'll Learn and Why 0:05
- Topics Overview
- Vocabulary 0:16
- Compatible Numbers
- Estimating by Rounding 1:08
- Estimate 36 + 6 + 58
- Estimate 94 - 35 - 42
- Estimating with Compatible Numbers 3:02
- Estimate 297 ÷ 17
- Estimate 9 Times 38
- Estimating for Reasonableness 4:13
- Example: Total Cost of the Items
- Extra Example 1: Estimating with Compatible Numbers 6:02
- Extra Example 2: Estimating by Rounding 7:05
- Extra Example 3: Estimating for Reasonableness 7:27
- Extra Example 4: Estimating for Reasonableness 9:15

1 answer

Last reply by: Professor Fung

Sat Jul 6, 2013 6:07 AM

Post by Han Jun Kim on July 2, 2013

In Extra Example 1 its 670/50 not 53...you didnt round the second number.... right?

1 answer

Last reply by: Ahmed Mahdi

Thu Oct 11, 2012 1:43 PM

Post by Eric Hill on June 19, 2012

We are new to educator.com are there any practice problems associated with each section other than the examples that are part of the lecture?