Algebra 1 Common Core Student Edition, Grade 8-9

Using Est imat ion

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To m ake sure th e answ er to a problem is reasonable, you can estim ate before you

calculate. If the answ er is close to your estim ate, th e answ er is probably correct.

Ex a m p l e 1

Estimate to find whether each calculation is correct,

a. C alcu latio n E stim ate b. C alcu latio n

$126.91 = $130

$14.05 « $10

+ $25.14 * +$30

372.85

-227.31

145.54

Estim ate

370

-2 3 0

140

$266.10 $170

I h e answ er is n o t close to the

estim ate. It is n o t reasonable.

The calculation is incorrect.

The answ er is close to the

estim ate. It is reasonable.

The calculation is correct.

For som e situations, like estim ating a grocery bill, you m ay n o t n e e d a n exact

answer. A front-end estimate will give you a good estim ate th a t is usually closer

to the exact answ er th a n an estim ate you w ould get by rou n d in g alone. Add the

front-end digits, estim ate th e sum of the rem aining digits by rounding, an d

th e n com bine sums.

Ex a m p l e 2

Tomatoes cost $3.54, squash costs $2.75, and lem on s cost $1.20. Estimate the

total cost of the produce.

Add the 3 .5 4 —* 0 .50 Estimate by rounding. Then add.

front-end digits. 2.75 —» 0 .8 0

+ 1.20 -> + 0.20

6 1 .50

Since 6 + 1.50 = 7.50, the total cost is ab o u t $7.50.

f —..................................

Ex e r c i se s

Estimate by rounding.

1. th e sum of $15.70, $49.62, and $278.01 2. 563 - 125


2. the sum of $163.90, $107.21, and $33.56 4. 824 - 467

Use front-end estim ation to find each sum or difference.

5. $1.65 + $5.42 + $9.89 6. 1.369 + 7.421 + 2.700 7. 9.563 -


6. 1.17 + 3.92 + 2.26 9. 8.611 - 1.584 10. $2.52 H

**\

2.480

$3.04 + $5.25

11. Ticket prices at an am u sem en t park cost $ 11.25 for adults an d $6.50 for
    children under 12. Estim ate th e cost for th ree children an d one adult.