Multiplying and dividing decimals

[Pages:13]Multiplying and Dividing Decimals

A key component to improving success on the GCSE Non-Calculator Exam!

On a calculator...

? 67 x 423 = ? 67 x 42.3 = ? 67 x 4.23 = ? 67 x 0.423 = ? What do you notice? ? Using the same digits can you find another

multiplication that gives the same answer as 67 x 4.23? ? Can you find another? And another?

Now without a calculator

39 x 8 = 312

Without using a calculator, write down the answers to these multiplications:

(i) 3.9 x 8 =

(ii) 39 x 0.8 =

(iii) 0.39 x 8 =

(v) 0.39 x 0.8 =

37 x 56 = 2072

Without using a calculator, write down the answers to these multiplications:

(i) 3.7 x 56 =

(ii) 37 x 5.6 =

(iii) 0.37 x 56 =

(v) 0.37 x 5.6 =

(iv) 3.7 x 5.6 =

(vi) 0.37 x 0.56 =

Multiplying Decimals

E.G.1 8 x 0.7

1. 8 x 7 = 56 2. 7 is 10 x bigger that 0.7, so 56 is 10 x too big 3. Divide 56 by 10

8 x 0.7 = 5.6

Multiplying Decimals

E.G.2 8.3 x 3.4

1. 83 x 34 = 2822 (I used the grid method, you can use

which ever method you prefer ? so long as it gets the right

answer!!) 2. 83 is 10 x bigger that 8.3 and 34 is 10 x bigger

than 3.4 so 2822 is 100 x too big 3. Divide 2822 by 100

8.3 x 3.4 = 28.22

Questions ? show all of your working out

a) 0.47 x 6

i) 9.6 x 0.09

b) 4.8 x 4

j) 4.8 x 0.25

c) 7 x 1.04

k) 11.3 x 3.12

d) 1.32 x 0.5

l) 21 x 1.45

e) 2.1 x 1.8

m) 9.85 x 1.67

f) 9.3 x 1.5

n) 0.57 x 0.342

g) 8.2 x 1.6

o) 0.23 x 7.85

h) 3.2 x 0.14

p) 15 .3 x 1.564

Questions ? show all of your working out

a) 0.47 x 6 = 2.82 b) 4.8 x 4 = 19.2 c) 7 x 1.04 = 7.28 d) 1.32 x 0.5 = 0.66 e) 2.1 x 1.8 = 3.78 f) 9.3 x 1.5 = 13.95 g) 8.2 x 1.6 = 13.12 h) 3.2 x 0.14 = 0.448

i) 9.6 x 0.09 = 0.864 j) 4.8 x 0.25 = 1.2 k) 11.3 x 3.12 = 35.256 l) 21 x 1.45 = 30.45 m) 9.85 x 1.67 = 16.4495 n) 0.57 x 0.342 = 0.19494 o) 0.23 x 7.85 = 1.8055 p) 15 .3 x 1.564 = 23.9292

On a calculator

? 420 ? 70 = ? 42 ? 7 = ? 4.2 ? 0.7 = ? 0.42 ? 0.07 = ? What do you notice?

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