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1-1 Using Estimation Strategies. Do Now: Round the following to the place of the underlined digit: 8 2 ,729 4 49 24,1 0 6 3, 5 28. Quick Tour of the Room. New Vocabulary. Compatible numbers: numbers that are easy to compute mentally ≈ Symbol that indicates estimation. Rounding.

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1 1 using estimation strategies

1-1 Using Estimation Strategies

Do Now: Round the following to the place of the underlined digit:

82,729

449

24,106

3,528

new vocabulary
New Vocabulary
  • Compatible numbers: numbers that are easy to compute mentally
  • ≈ Symbol that indicates estimation
rounding
Rounding
  • The span of an eagle ray’s fin is 3.27 m. The span of her baby’s fin is 0.88m. Estimate the difference between the spans. Round to the nearest whole number before you find the difference.
  • 3.27−0.88≈3−1  Round to the nearest whole number

≈2 Subtract

estimate
Estimate.
  • First round to the nearest whole number
    • 1.75+0.92
    • 14.34−7.8
    • 4.90×6.25

2+1=3

14−8=6

5×6=30

front end estimation
Front End Estimation
  • Add the “front-end” digits, ignoring the decimals.
  • Estimate the decimals.
  • Add the decimal estimate to the front-end sum.
example
Example

5.45

9.89

3.53

6.03

Front-end: 5 + 9 + 3 + 6 = 23

  • Decimals:
  • .89 is close to 1.
  • .03 is close to 0.
  • .45 + .53 is close to 1.
  • 1 + 0 + 1 = 2

+

About 25

Put the front-end with the decimal: 23 + 2 = 25.

compatible numbers go together
Compatible numbers go together!
  • Compatible
  • 54 and 9
  • 16 and 4
  • 32 and 8
  • 12 and 3
  • 54 and 6
  • 18 and 2
  • Not compatible
  • 17 and 2
  • 35 and 9
  • 15 and 4
  • 27 and 8
  • 24 and 5
  • 15 and 6
estimating using compatible numbers
ESTIMATING Using Compatible Numbers
  • Overbidding

52 ÷ 6 overbid 52 count up: 53 no

54 yes

32 ÷ 5 overbid 32 count up: 33 no

34 no

35 yes

7 ÷ 4 overbid 7 count up: 8 yes

Of course, you can use the multiples of the factor … multiplication facts.

estimating using compatible numbers1
ESTIMATING Using Compatible Numbers
  • Underbidding

52 ÷ 6 underbid 52 count down: 51 no

50 no

49 no

48 yes

32 ÷ 5 underbid 32 count down: 31 no

30 yes

7 ÷ 4 underbid 7 count down: 6 no

5 no

4 yes

Of course, you can use the multiples of the factor … multiplication facts.

compatible numbers
Compatible Numbers

Underbidding

Overbidding

20

17 ÷ 5 4

36

29 ÷ 9 4

48

42 ÷ 8 6

  • 17 ÷ 5 3

15

  • 29 ÷ 9 3

27

  • 42 ÷ 8 5

40

try these
TRY THESE

Use paper and pencil.

Check on next page.

  • 73 ÷ 2
  • 139 ÷ 2
  • 236 ÷ 7
  • 653 ÷ 9

Estimate

  • Did you overbid?
  • Did you underbid?
  • Did you change numbers to zero?
check your work
Check your work!

80 40 140 70

73 ÷ 2 139 ÷ 2

70 35 120 60

280 40 720 80

236 ÷ 7 653 ÷ 9

210 30 630 70

minute time
Minute Time!
  • Get ready, get set…
test time
Test Time
  • Number your paper 1-10