Estimate It!
Decimal Multiplication
Decimal Division
Equivalent or Not?
Real World Decimals :)
100
What is the best estimate for 4.98 + 7.12 ?
Be prepared to explain your choice.
A) 9 B) 10 C) 12 D) 15
C) 12
4.98 rounds to 5
7.12 rounds to 7
5+7 = 12
100
2.1 x 3
6.3
100
45.6 ÷ 3
15.2
100
4 ÷ 20
and
8 ÷ 40
Yes! Dividend and divisor both multiplied by 2
100
A 1.5 liter bottle of grapefruit juice costs $2.85
A 2.5 liter bottle of apple juice costs $4.25
Which bottle has the lowest cost per liter?
Grapefruit - $1.90 per liter
Apple - $1.70 per liter
Apple has the lower unit cost. Better deal.
200
What is the best estimate for 6.02 - 2.97 ?
Be prepared to explain your choice.
A) 1 B) 3 C) 5 D) 9
B) 3
6.02 rounds to 6
2.97 rounds to 3
6 - 3 = 3
200
3.5 x 1.2
4.20 or 4.2
200
Using Long Division, find the quotient:
1 ÷ 8
0.125 or 125/1000
200
0.3 ÷ 60
and
3 ÷ 6
No!
For division, they both have to be multiplied by the same factor. The dividend was multiplied by 10 and the divisor was multiplied by 1/10
200
A 1.5 liter bottle of grapefruit juice costs $2.85
How much would 5 liters of grapefruit juice cost?
$9.50
300
What place should the product of 3.02 x 1.98 end in?
a) hundredths
b) thousandths
c) ten thousandths
d) hundred thousandths
c) ten thousandths
There are four combined places after the decimal in the factors, so the product should have four places after the decimal (ten thousandths).
300
Find the missing factor:
9 x ? = 7.2
0.8
Pat yourself on the back if you used prior knowledge that 9 x 8 = 72 to reason through your answer.
300
24.48 ÷ 0.6
40.8
300
0.00005 ÷ 0.02567
and
0.05 ÷ 25.67
Yes. Both multiplied by 1000.
300
A small popcorn costs $5.25 and contains 6.5 cups.
A regular popcorn costs $8.40 and contains 10.5 cups.
Which size has a better value?
(Round all decimals to the nearest hundredth)
Small - $0.81 per cup
Regular - $0.80 per cup
The regular is a better value by $0.01
400
Without calculating, which product will be closest to 50?
a) 4.9 x 4.825
b) 4.78 x 0.9837
c) 4.8 x 9.82158
d) 0.3 x 100
c) 4.8 x 9.82158
4.8 rounds to 5
9.82158 rounds to 10
5 x 10 = 50
400
3.33 x 1.4
4.662
400
72.45 ÷ 2.5
28.98
400
569.308 ÷ 7.8
and
569,308 ÷ 780
No. Dividend multiplied by 1000. Divisor multiplied by 100
400
Five Star is selling a 6-pack of notebooks for $8.94.
Muji has a 10-pack for $14.20.
What is the difference in cost per notebook from each brand?
Five Star - $1.49 per notebook
Muji - $1.42 per notebook.
1.49 - 1.42 = 0.07
A difference of 7 cents.
500
Bryce says "The answer to 5.05 x 2.03 will end in the hundredths place because both factors have two places after the decimal."
Explain what mistake Bryce made and provide the correct product.
10.2515
Bryce forgot that we have to add the number of places after the decimal from each product.
500
Najla says to answer 4.2 x 5.1 she can find the product of 42 x 51 and then just move the decimal to the left two times.
Explain why Najla's method for multiplying decimals works. Hint: what does "moving the decimal left" mean in math terms.
Example Answer: Najla multiplied both of her factors by 10 to turn them into whole numbers.
At the end of her problem she can divide the product of 42 and 51 by 100 to undo that multiplication and find her answer. Dividing by 100 = moving the decimal to the left two times.
500
Ana Lis says that to complete 0.2 ÷ 9.87 she has to multiply both her dividend and divisor by 100.
Do you agree? Why or why not?
Find your quotient and round to the nearest ten thousandths place.
0.0203
Disagree! As long as Ana Lis gets rid of the decimal in the divisor, she can complete Long Division. To get rid of the decimal in the divisor, the decimal only needs to move right one time (aka. multiply by 10 = 2 ÷ 98.7)
500
What are some methods you could use to find out if two division expressions are equivalent?
- comparing quotients
- creating equivalent fractions
- tracking decimal movements
500
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