3.1 – 3.4 Pre-Test

Please grab your clicker and a

scrap piece of paper!!

CHAPTER 3: DECIMALS AND EQUATIONS

Section 3.1: Rounding & Estimating

Rounding!!!!

Practice!!

Round 4.2683 to the nearest tenth.

4.2683

Is the number after the tenths place 5 or larger?

Yes, so we round up!

4.3!!!

Round 4.2683 to the nearest Integer.

4.2683

Is the number after the Integers place 5 or larger?

No, so we do not round up!

4!!!

You Try!!

Round 4.2683 to the nearest hundredth.

4.2683

Is the number after the hundredths place 5 or larger?

Yes, so we round up!

4.27!!!

Round 4.2683 to the nearest thousandth.

4.2683

Is the number after the Integers place 5 or larger?

No, so we do not round up!

4.268!!!

Estimating!!!You can estimate an answer before you calculate it to make sure your answer is reasonable. If the answer is close to the estimate, then you know it is probably correct?

The symbol “≈” means “is approximately equal to”.

Example:Estimate 127 ≈ 130

Practice!!

Calculation Estimate$135.95 ≈$140$ 15.90 ≈$ 20+$24.05 ≈ $ 20$275.90$180

The answer is not close to the estimate. The answer is not reasonable.

Calculation Estimate 464.90 ≈ 460- 125.73 ≈ -130 339.17 330

The answer is close to the estimate. The answer is reasonable.

Estimate to find if the answer is reasonable.

Estimate – You Try!!355.302 + 204.889 360 + 200 ≈ 560

453.56 – 230.07 450 – 230 ≈ 220

632.76 + 214.45 630 + 210 ≈ 840

427.35 – 182.66 430 – 180 ≈ 250

Front-End EstimatingFront-end estimation is often closer to the exact sum than estimation by rounding. First add the front-end digits. Round to estimate the sum of the remaining digits.

1.10.10 1.73.70+2.71 .70 4 + 1.50

Total ≈ 5.50

Front-End Estimating – You Try!!

6.75.80 2.20.20+9.58 .60 17 + 1.60

Total ≈ 18.60

1.07.10 2.49.50+7.40 .40 10 + 1.00

Total ≈ 11.00

Clustering

You can also use clustering to estimate the sum of several numbers that are close to one value.

Estimate the following using clustering:15.35 + 16.05 + 14.90 +15.05

All the values are around 15. So we do 15 times 4!

15(4) ≈ 60!!!!

Clustering – You Try!!!44.87 + 42.712 + 43.5

All the values are close to 43.

43(3) ≈ 129

26.7 + 26.2 + 24.5 + 25.25 + 23.9

All the values are around 25.

25(5) ≈ 125

Homework!!!

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