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Multiplying & Dividing DecimalsPowerPoint Presentation

Multiplying & Dividing Decimals

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Multiplying & Dividing Decimals

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Multiplying & Dividing Decimals

September 18, 2012

Modeling:

To model multiplication of decimals:

1.Shade in vertically the number of boxes represented by the first decimal.

2.Shade in horizontally the number of boxes represented by the second decimal.

3.The boxes shaded twice will give you the answer to the problem.

Shade four of the columns.

Shade five of the rows.

Count how many squares are double shaded.

20 squares are shaded, so the answer is 0.2.

Shade two of the columns.

Shade one of the rows.

Count how many squares are double shaded.

2 squares are shaded, so the answer is 0.02.

To Multiply Decimals:

1.Ignore the decimals.

2.Multiply as normal.

3.Count the number of digits to the right of all decimals in the problem.

4.Starting at the end of the answer. Move the decimal to the left the number of spots that you counted from step 3.

Since there is one digit to the left of the decimal, we will move the decimal over right once in our answer.

5) The food service workers at Mountain Springs Elementary School begin their work at 5:27 a.m. and finish their days at 10:27 a.m. They work five days a week. If they make $7.21 per hour, how much do they make in a week?

5) The food service workers at Mountain Springs Elementary School begin their work at 5:27 a.m. and finish their days at 10:27 a.m. They work five days a week. If they make $7.21 per hour, how much do they make in a week?

5:27 to 10:27=5 hours

721

x 5

$36.05/day

x 5 days

$180.25 each week

To Divide Decimals:

1.Move the decimal in the divisor to the end.

2.Move the decimal in the dividend the same number of places.

3.Bring the decimal point up.

4.Divide as usual.

quotient

divisor

dividend

6) 22.890.4 9.156 4 91.56-8 11- 8 35-32 36-36 0

7.

= 9.8 28 98 280

7.

8. The members of the Drama Club make a profit of $0.42 on each box of cookies they sell. Their profit for the first week of sales was $50.40. How many boxes did they sell?

8. The members of the Drama Club make a profit of $0.42 on each box of cookies they sell. Their profit for the first week of sales was $50.40. How many boxes did they sell?120 Boxes

9.Equal-sized cartons were lined up end to end on a 2.4 meter long shelf. Each carton was 0.4 meter wide. How many cartons were place on the shelf?

9.Equal-sized cartons were lined up end to end on a 2.4 meter long shelf. Each carton was 0.4 meter wide. How many cartons were place on the shelf?6 cartons