1-1 Using Estimation Strategies

Do Now: Round the following to the place of the underlined digit:1.82,7292.4493.24,1064.3,528

Quick Tour of the Room

New VocabularyCompatible numbers: numbers that are easy to

compute mentally≈ Symbol that indicates estimation

Rounding Front-end Estimation

Compatible Numbers

1.3+2.4≈ 3 1.2 + 3.7 ≈5 26÷4≈5 1 + 2 = 3 1+3+4

0+1=14+1=5

25÷5=5

RoundingThe 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.First round to the nearest whole number

1.75+0.9214.34−7.84.90×6.25

2+1=314−8=65×6=30

Front End EstimationAdd the “front-end” digits, ignoring the

decimals.Estimate the decimals.Add the decimal estimate to the front-end sum.

Example5.459.893.536.03+

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

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

About 25

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

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 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

Underbidding 17 ÷ 5 3 15

29 ÷ 9 3 27

42 ÷ 8 5 40

Overbidding 20 17 ÷ 5 4

36 29 ÷ 9 4

48 42 ÷ 8 6

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!

80 40 140 7073 ÷ 2 139 ÷ 270 35 120 60

280 40 720 80236 ÷ 7 653 ÷ 9 210 30 630 70

Minute Time!Get ready, get set…

Test TimeNumber your paper 1-10