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DecimalComputationStudyGuide**ExtraCredit!**
Estimates:
Wedoestimatestodetermineifanpossibleanswerisareasonablesolution.
• Foraddition,subtraction,andmultiplication–wecompleteanestimateby
roundingallnumberstothesameplacevalueandthencomputing.
RoundingExample:
12.325x3.94!12x4=48
•
Fordivisionweusedcompatiblenumberstoestimate.Weroundthe
divisor,thenwechooseacompatibledividendthatiseasytocomputewith
theroundeddivisor.
CompatibleNumbersExample:
47.85÷9.23!45÷9=5
PracticeEstimatingtheFollowingProblems:
1.25.4x3.1
2.121x7.3
3.57÷8.9 4.40.125÷6.1
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AddingandSubtractingDecimals:
• Lineupthedecimals.Annex(add)zerosasneededtomakeproblemline
up.
• Addorsubtractaswelearnedbefore.
• Becarefulwhenborrowingfromhigherplacevalueswithsubtraction!
• Examples:
AdditionandSubtractionPractice:
5.124.3+15.7
6.263.4+199.06
7.52.1-31.47
8.82–67.18
MultiplyingDecimals
Tomultiplyyouwilllineupyourproblemneatly(butwedonothavetolineup
decimals).Multiplyeachplacevalueyouthrough.Rememberwhenyougotothe
secondnumberholdaplacewithazerointheproduct.Whendone,counttheplaces
aftertheThen,add.Seetheexamplebelow.
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MultiplicationPractice:
9.0.52x3
10.0.014x3.7
11.1.03x1.005
12.5.04x3.2
Division
• Ifdividing2wholenumbersjustdolongdivisionlikeyoustartedlearningin4th
grade.Then,ifyouneedtoaddzerosafterthedecimaltocompletetheanswer
dothat.Wewillnotgiveremaindersasanswers.Seetheexamplebelow.
126÷5
• Ifdividingdecimalbyawholenumber,dothesamethingasabove,except
remembertoputthedecimaldirectlyaboveitinthequotient.Seebelow.
11.75÷5
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•
Fordecimalsinthedivisor,movethedecimalthenumberofplacestotheright
inthedivisortomakeitawholenumber.Thenmovethedecimalthesame
amountofplacesinthedividend.Then,solveliketheotherdivisionproblems.
DivisionPracticeProblems:
13.23451÷3
14.23.48÷4
15.569.2÷3.2
16.1584÷4.5
WordProblems
Youwillhavewordproblemsthatyouwillneedtodeterminewhatproblemtowrite
tosolve.Thiscouldbeforaddition,subtraction,multiplication,ordivision.Trythe
followingproblems.
17.Acartravels57.9milesperhourfor3.2hours.Estimatethenumberofmiles
driven.
18.Aloafofbreadcosts$1.79.Howmuchwouldfiveloavescost?
19.Amarathonraceis26.2mileslong.Joeranthemarathonin2.5hours.On
average,howmanymilesdidherunperhour.Roundtothenearesttenthofamph.
20.Howmanydimesarein$8,590?