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Topic 7 Estimating
Decimal Products and
Quotients
Mrs. Fillat
5th Grade Math Enrichment
Lesson Objectives
By the end of today’s lesson you will be able By the end of today’s lesson you will be able to:to:
1)1)Estimate products using mental math.Estimate products using mental math.
2)2)Estimate quotients using compatible Estimate quotients using compatible numbers.numbers.
Estimating Products
Estimate each product.Estimate each product.
1) 7.65 1) 7.65 ×× 3.2 3.2 2) 6.43 2) 6.43 ×× 4.7 4.7
Estimating Products
Estimate each product.Estimate each product.
3) 4.563) 4.56××7.02 4) 6.37.02 4) 6.3××9.2 5) 3.299.2 5) 3.29××5858
≈ ≈ 3535 ≈ 54≈ 54≈180≈180
Estimating Products
Josh bought 3 yards of fabric to Josh bought 3 yards of fabric to make a flag. Fabric costs $5.35 per make a flag. Fabric costs $5.35 per
yard. The clerk says his total is yard. The clerk says his total is $14.95 before tax. Did the clerk $14.95 before tax. Did the clerk
make a mistake?make a mistake?
Estimating Products
You buy 24 donuts from the Donut You buy 24 donuts from the Donut Emporium in Plano. Each donut costs Emporium in Plano. Each donut costs
$.98 . Estimate the cost before tax for 2 $.98 . Estimate the cost before tax for 2 dozen donuts?dozen donuts?
≈ ≈ $24$24
Objective #1
Can you… Can you…
~ estimate products using mental ~ estimate products using mental math?math?
Let’s Check…Let’s Check…
Check for Understanding
Estimating Quotients
6 ÷ 3 = 26 ÷ 3 = 2
The first number is the The first number is the dividenddividend..
The second number is the The second number is the divisordivisor..
The number after the = sign is the The number after the = sign is the quotientquotient..
Estimating Quotients
Name the following:Name the following:
18 ÷3 = 618 ÷3 = 6
3 is the: 3 is the:
18 is the:18 is the:
6 is the:6 is the:
Estimating Quotients
defdefnn: : compatible numberscompatible numbers: :
-numbers easy to divide mentally-numbers easy to divide mentally
*When dividing, you can use *When dividing, you can use compatible numbers to estimate compatible numbers to estimate quotientsquotients
Estimating Quotients
When you estimate the quotient:When you estimate the quotient:
1)1)Round the Round the divisordivisor..
2)2)Round the Round the dividenddividend to a to a compatible number.compatible number.
Estimating Quotients
Estimate the quotient using Estimate the quotient using compatible numbers.compatible numbers.
1)1) 14.9 ÷ 2.8 14.9 ÷ 2.8 2) 25.3 ÷ 4.92) 25.3 ÷ 4.9
Estimating Quotients
Estimate the quotient using compatible Estimate the quotient using compatible numbers.numbers.
3) 35.8÷3.8 4) 29.4÷1.8 5) 49.6÷4.43) 35.8÷3.8 4) 29.4÷1.8 5) 49.6÷4.4
≈ ≈ 9 ≈ 15 ≈ 109 ≈ 15 ≈ 10
Estimating Quotients
The cost to ship 1 yearbook is $3.12. The total The cost to ship 1 yearbook is $3.12. The total cost for a shipment was $62.40. Estimate cost for a shipment was $62.40. Estimate how many books were in the shipment. how many books were in the shipment.
1)1)Round the divisor.Round the divisor.
2)2)Round to a multiple of 3.Round to a multiple of 3.
3)3)Find the quotient.Find the quotient.
Estimating Quotients
Use estimation. Is each quotient Use estimation. Is each quotient reasonable?reasonable?
1) 17.931÷8.34 =2.151) 17.931÷8.34 =2.15 2) 2) 31.423÷5.94=3.2931.423÷5.94=3.29
Estimating Quotients
Use estimation. Is each quotient reasonable?Use estimation. Is each quotient reasonable?
3) 318.274÷4.07=78.23) 318.274÷4.07=78.2 4) 4) 41.09÷6.88=5.1241.09÷6.88=5.12
Reasonable Not Reasonable Reasonable Not Reasonable
Objective #2
Can you… Can you…
~ estimate quotients using ~ estimate quotients using compatible numbers?compatible numbers?
Let’s Check…Let’s Check…
Check for Understanding
Next, compare answers with a neighbor.Next, compare answers with a neighbor.
18) ≈5 19) ≈6 21) ≈1518) ≈5 19) ≈6 21) ≈15
Estimating Decimal Products and Quotients
Ask yourself if you can do the following:Ask yourself if you can do the following:
1)1)Estimate products using mental math.Estimate products using mental math.
2)2)Estimate quotients using compatible Estimate quotients using compatible numbers.numbers.
