8. Multiplying Decimals · Multiplying Decimals 3.21 x 0.04 0.1284 There are a total of four digits to the right of the decimal points. There must be four digits to the right of the

8. Multiplying Decimals December 14, 2015

Warm Up 65th day of school 12‐14‐15

1. 5.6 104

2. 8 10,000

3. 56.48792 106

4. 0 100,000

5. 9.872 10

6. 143.5240 100.

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Multiplying Decimals


We can use two strategies:

1. Estimate what the product will be if you rounded the factors. The actual product will be close to that estimate. Ex. 9.458 6.542 will be approximately 63.

2. Count the number of digits to the right of the decimal points in both (all) factors. That is how many decimal places there will be in the product. Ex. 9.125 7.84 will have 5 decimal places.

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Strategy #1:

Estimate the following products. Find a range of numbers the product should be between .

A. 12.35469 6.4521 = ___________

B. 29.6254 5.1245 = ___________

C. 122.8523 4.1973 = ___________


Strategy #2:

How many decimal places after the decimal point will be in the following products?

D. 958.5214 9.62 = ___________

E. 63.2 185.524 = ___________


3.21x 0.040.1284

There are a total of four digits to the right of the decimal points.

There must be four digits to the right of the decimal point in the answer.

}

23.2x 4.04

928

93.728

} 92800

There are a total of three digits to the right of the decimal points.

There must be three digits to the right of the decimal point in the answer.

EXAMPLETRY THESE.Complete these products and then check with your neighbor.

A) 3.52 B) 8.31 x 4.21 x 0.008 352 0.06648 7040

140800 14.8192

Practice


7.0045 D) 3.214x 0.012 x 0.0034 140090 12856 700450 96420 0.0840540 0.0109276

C)1 Multiply 0.42 x 0.032

0.01344

2 Multiply 3.452 x 2.1

7.2492

3 Multiply 53.24 x 0.089

4.73836


4 Multiply 4.0156 x 7.831.32168

5 Multiply 0.012 x 0.210.00252

Find the area... Recall the formula for finding area of a rectangle

2.56 cm

4 cm

A= length times width

Find the area... Recall the formula for finding area of a square

8.0564 mi

A= L W


Find the area... Recall the formula for finding area of a rectangle

4.0159 in

8.9 in

Find the area... Recall the formula for finding area of a triangle

15.75 in

1.362 in

A = b h12

0.053 (0.05)3

Decimals Raised to an Exponent

Meansthe same as

so we are multiplying 0.05 to itself 3 times!

1.22

1.23

1.24


3.52

3.51 0.92

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8. Multiplying Decimals · Multiplying Decimals 3.21 x 0.04 0.1284 There are a total of four digits to the right of the decimal points. There must be four digits to the right of the