1 1 Using Estimation Strategies Do Now Round

New Vocabulary Compatible numbers: numbers that are easy to compute mentally ≈ Symbol that

Rounding The span of an eagle ray’s fin is 3. 27 m. The span

Estimate. First round to the nearest whole number 1. 75+0. 92 14. 34− 7.

Front End Estimation Add the “front-end” digits, ignoring the decimals. Estimate the decimals. Add

Example 5. 45 + Front-end: 5 + 9 + 3 + 6 = 23

Compatible numbers go together! Compatible Not compatible 54 and 9 17 and 2 16

ESTIMATING Using Compatible Numbers Overbidding 52 ÷ 6 overbid 52 count up: 53 no

ESTIMATING Using Compatible Numbers Underbidding 52 ÷ 6 underbid 52 count down: 51 no

Compatible Numbers Underbidding 17 ÷ 5 3 3 40 5 4 36 29 ÷

TRY THESE Use paper and pencil. Check on next page. 73 ÷ 2 139

Check your work! 80 40 73 ÷ 2 70 280 70 139 ÷ 2

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1 -1 Using Estimation Strategies Do Now: Round the following to the place of the underlined digit: 1. 82, 729 2. 449 3. 24, 106 4. 3, 528

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New Vocabulary Compatible 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+3+4 0+1=1 4+1=5 25÷ 5=5 1 +2=3

Rounding The span of an eagle ray’s fin is 3. 27 m. The span of her baby’s fin is 0. 88 m. Estimate the difference between the spans. Round to the nearest whole number before you find the difference. 3. 27− 0. 88≈3− 1 ≈2 Round to the nearest whole number Subtract

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 Add the “front-end” digits, ignoring the decimals. Estimate the decimals. Add the decimal estimate to the front-end sum.

Example 5. 45 + Front-end: 5 + 9 + 3 + 6 = 23 9. 89 Decimals: 3. 53 • . 03 is close to 0. 6. 03 • 1 + 0 + 1 = 2 About 25 • . 89 is close to 1. • . 45 +. 53 is close to 1. Put the front-end with the decimal: 23 + 2 = 25.

Compatible numbers go together! Compatible Not compatible 54 and 9 17 and 2 16 and 4 35 and 9 32 and 8 15 and 4 12 and 3 27 and 8 54 and 6 24 and 5 18 and 2 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

Compatible Numbers Underbidding 17 ÷ 5 3 3 40 5 4 36 29 ÷ 9 27 42 ÷ 8 20 17 ÷ 5 15 29 ÷ 9 Overbidding 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 73 ÷ 2 70 280 70 139 ÷ 2 35 40 236 ÷ 7 210 140 120 60 720 80 653 ÷ 9 30 630 70

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