D3-L15 Decimals Practice : Multiplication and Division

DECIMAL NUMBERS – D4 (~70 min)    Date/Time:               Tutor:             

(Part 1) Revise(15-20mins)                                               Start Time:                 

1. Multiplication and Division of Decimals (by 1 digit whole number, up to 2.d.p.)

(Part2) Practice (30-40mins)

Complete the Multiplication Tables (~5mins)

3x2=	4x2=	5x2=	6x2=	7x2=	8x2=	9x2=	12x2=
3x3=	4x3=	5x3=	6x3=	7x3=	8x3=	9x3=	12x3=
3x4=	4x4=	5x4=	6x4=	7x4=	8x4=	9x4=	12x4=
3x5=	4x5=	5x5=	6x5=	7x5=	8x5=	9x5=	12x5=
3x6=	4x6=	5x6=	6x6=	7x6=	8x6=	9x6=	12x6=
3x7=	4x7=	5x7=	6x7=	7x7=	8x7=	9x7=	12x7=
3x8	4x8	5x8	6x8	7x8	8x8	9x8	12x8
3x9=	4x9=	5x9=	6x9=	7x9=	8x9=	9x9=	12x9=

(I) Decimals (~20 mins)                  Start Time:                

Give your answer correct to 1 decimal place.

1.     2.84 x 9

2.     7 x 30.12

3.     26.15 x 8

4.     0.75 ÷3

5.    47.36 ÷ 8

6.    28.16÷4

7.   Find the value of 10.4 x 30

8.  Divide 1.7 by 7 correct to 2 decimal places.

9.  Estimate (a) 4.3 ¸6. Then find the actual value correct to 1 decimal place.

End Time:                          Mark:        /10

(II) PSLE/Word Problems (~25 mins)                   Start Time:                 

10.  A running track is 0.4 km long. James jogs 6 laps. What is the total distance that James jogs?

11.  Linda bought 3 oranges and a mango for $4.05. The mango cost $1.50. How much did each pineapple cost?

12.  Ken had $20. He bought 8 cans of drinks at 0.75 each. How much money did Ken have left?

For questions 13-14

3 groups of students collected $198 for their outing. This amount included $30 from their teacher. 

13.   How much did the group collected? 

14.   How much did each groups of students paid?

15.  Sally has $204.80. She has 4 times as much money as Eric. How much more money does Sally have than David?

16*.  Find the value of 0.46 x 70

17. Peter wanted to buy 6 books of the same price but found that he was short of $10.50. In the end, he bought 4 of the books and had $6 left. Find the cost of each book. 

18. Mindy sold 4 times as many headphone as mobile phone and collected a total of $8400. Each mobile phone costs $325 more than an headphone. The amount collected for all the headphones sold was $3480 more than the amount collected for all the mobile phones sold. How many mobile phones did Mindy sell?

End Time:                  Total Mark:      

Extra Practice

1.   Multiply. Give your answer correct to 1 decimal place.

            (a)  2.84 x 4

            (e)  3 x 6.05

2.   Divide. 

            (b)  6.79 ÷7

            (c)  20.45 ÷5

            (d)  27.36 ÷9

            (e)  20.04 ÷4

3.  Ronald bought two cakes for $2.40 and one packet of drink for $0.90. He then bought another 5 cakes and 3 packets of drinks for his friends. How much did he pay altogether? 

4.  Mindy was given $3 pocket money every day of the week. She spent $2.60 per day from Monday to Friday and saved the rest. She saved all her pocket money on Saturday and Sunday. Starting on a Monday, how many days did it take her to save $50?

Answer Keys

1.   25.56

2.   210.84

3.   20.92

4.   0.25

5.   5.92

6.   7.04

7.   312

8.   0.24

9.   ~0.7, 0.72

10.   2.4 km

11.   $0.85

12.   $2

13.   $168

14.   $56

15.  $153.60

16.  3.22

17.  $13.25

18.  3

D5 Decimals : Multiplication and Division

DECIMAL MULTIPLICATION

              

One notebook weighs 1.25kg

3 notebooks weigh

             1.25 + 1.25 + 1.25 = 3.75kg

             1.25 x 3 = 3.75kg

5 notebooks weigh

            1.25 + 1.25 + 1.25 + 1.25 + 1.25 = 4.25kg

            1.25 x 5 = 4.25

DECIMAL NUMBERS multiply by 10s, 100s, 1000s

When a decimal number is MULTIPLY by 10, 
the decimal value shifts by ONE PLACE to the RIGHT.

            1 “shift” of decimal point to the right is equal to multiply by 10.

Examples:

          

Practice

Find    (a) 1.5 x 3000      

           (b)  0.013 x 1000  

           (c)  2.08 x 10

MULTIPLICATION METHOD

The method to do multiplication without using addition:

Method
Example:

            132.4 x 0.02

Step1: Multiply without decimal point

                        1324 x 2 = 2648

Step2: Count number of decimal places

                        132.4 has 1

                        0.02 has 2

            Total = 3 decimals

Step3: Place decimal places in answer

             

How to explain the method?

  Given Number: 132.4 to multiply by 10 = 1324 {shift 1 to right}

                                    0.02 to multiply by 100 = 2 {shift 2 to right}

            1324 x 2 = 2648

   Now, we need to shift 3 places to the left since we shift 3 to right

            2648 shift 3 to left = 2.648

DIVISION

DIVIDING DECIMAL NUMBERS BY 10s, 100s, 1000s

When a decimal number is divided by 10,

        the decimal value shifts LEFT by one place.

<Divide by 10 is equal to 1 LEFT shift decimal point;

                100 -> 2 LEFT shifts>

Example

         

Practice

     (1)  24.6 ÷ 1000                   (2) 24700 ÷ 10                     (3) 38.09 ÷ 1000    

DIVISION METHODS

Remember:         10/10 = 1
                                 100 / 100 = 1

Method 1 (Remove all decimal places)

Example

            Find 1.86

                      0.3

Step1: Multiply by multiple of 10 to remove decimal places

            1.86  x 100

              0.3  x 100

Step2: Do the division

         = 186/30

         =  62/10

         =   6.2

Method 2 (Remove denominator/divisor decimal places)

            Find 1.84

                      0.4

Step1: Multiply denominator by multiple of 10 to remove decimal places

            Find 1.84 x10 = 18.4

                      0.4 x10      4

Step2: Do long division

                             4.6

                      4 )18.4

                         - 16

                             2.4

                          -  2.4

                                0