estimate

EstimationStrategies

Sometimesyoudonotneedtoknowtheexactanswertoaproblem,

e

instances,youcanu

reveraldifferentmethodsof

nmethodistou

rounding.

EstimatebyRounding

Estimatebyrounding.

1189.2×315.6

Roundeachnumbertothe

ltiply.

189.2→200

_______

×6.513→

______

×300

60,000

Theproductisabout60,000.

2354

1_

5

+86

2_

3

Roundeachnumbertothe

d.

354

1_

5

→450

______

+86

2_

3

→

_____

+70

520

Thesumisabout520.

ringworksbestwithnumbersthatall

roundtoapproximatelythesamenumber.

EstimatebyClustering

Estimatebyclustering.

331

1_

4

+61

2_

5

+41

5_

6

+51

3_

8

Allofthenumbersareclo

refournumbers.

Thesumisabout4×15or60.

499.6+97.83+102.18+100.101+99.90

Allofthenumbersarecloto100.

Therearefivenumbers.

Thesumisabout5×100or500.

Compatiblenumbersarenumbersthatareeasytocomputewithmentally.

EstimatebyUsingCompatibleNumbers

Estimatebyusingcompatiblenumbers.

576.36÷24.73

76.36iscloto75,and24.73is

cloto25.

3

37.42

63.67→5275

Thequotientisabout3.

67

3_

8

+12+02

2_

3

Thefractions

3_

8

dna

2_

3

otesolcera

1_

2

.

7

1_

2

+12+02

1_

2

=7+12+20+(1_

2

+

1_

2

)

=39+1or40

Thesumisabout40.

Astrategythatworkswellforsomeadditionandsubtractionproblems

rategyinvolvesaddingorsubtractingthe

erosfortheremainingdigits.

UFront-EndEstimation

Ufront-endestimationtofindanestimate.

75,283+3,634

5,283→5,000

_______

+3436,→

_______

+3,000

88,000

Thesumisabout8,800.

8118.1-57.5

118.1→110.0

______

-55.7→

______

-50.0

660.0

Thedifferenceisabout61.