GCSE Maths Number Standard Form

Multiplying and Dividing in Standard Form

# Multiplying and dividing in standard form

Here we will learn about multiplying and dividing numbers in standard form including how to multiply, divide and square numbers in standard form.

There are also multiplying and dividing numbers in standard form worksheets based on Edexcel, AQA and OCR exam questions, along with further guidance on where to go next if you’re still stuck.

## What is multiplying and dividing in standard form?

Multiplying and dividing numbers in standard form is where we multiply and divide integers and decimals and apply the laws of indices to simplify the powers of ten. You also need to check that your final answer is in standard form.

E.g.

$(4\times10^{3})\times(2\times10^{6})$

$4\times2 = 8$

$10^{3}\times10^{6}\quad=\quad10^{9}$

$(4\times10^{3})\times(2\times10^{6})\quad=\quad8\times10^{9}$

E.g.

$(8\times10^{9})\quad \div \quad(2\times10^{6})$

$8 \div2 = 4$

$10^{9}\quad \div \quad10^{6}\quad=\quad10^{3}$

$(8\times10^{9})\quad \div \quad(2\times10^{6})\quad=\quad4\times10^{3}$

There are many applications of multiplying and dividing standard form numbers which includes applying it to area, volume, surface area, equations and Pythagoras’ theorem.

## How to multiply and divide in standard form

In order to multiply and divide numbers in standard form:

1. Multiply or divide the integers or decimal numbers.
2. Multiply or divide the powers of ten by adding or subtracting the indices.
3. Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

## Multiplying and dividing standard form examples

### Example 1: multiplying numbers in standard form

Work out:

$(3 \times 10^{4}) \times (2 \times 10^{5})$

1. Multiply or divide the integers or decimal numbers.

$3 \times 2 = 6$

2Multiply or divide the powers of ten by adding or subtracting the indices.

$10^{4} \times 10^{5} = 10^{9}$

3Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

$6 \times 10^{9}$

This number is already in standard form.

### Example 2: multiplying numbers in standard form

Work out:

$(3 \times 10^{5}) \times (6 \times 10^{-2})$

Multiply or divide the integers or decimal numbers.

Multiply or divide the powers of ten by adding or subtracting the indices.

Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

### Example 3: dividing numbers in standard form

Work out:

$(8 \times 10^{7}) \div (2 \times 10^{5})$

Multiply or divide the integers or decimal numbers.

Multiply or divide the powers of ten by adding or subtracting the indices.

Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

### Example 4: dividing numbers in standard form

Calculate:

$(3 \times 10^{4}) \div (6 \times 10^{-3})$

Multiply or divide the integers or decimal numbers.

Multiply or divide the powers of ten by adding or subtracting the indices.

Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

### Example 5: squaring numbers in standard form

Calculate:

$(8 \times 10^{4})^{2}$

Multiply or divide the integers or decimal numbers.

Multiply or divide the powers of ten by adding or subtracting the indices.

Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

### Example 6: cubing numbers in standard form

Calculate:

$(6 \times 10^{4})^{3}$

Multiply or divide the integers or decimal numbers.

Multiply or divide the powers of ten by adding or subtracting the indices.

Write the solution in standard form, checking that the first part of the number is [katex]\pmb{1\leq{x}\lt10}[/katex].

### Common misconceptions

• Multiplying the powers

When multiplying numbers in standard form, a common mistake is multiplying the powers rather than adding the powers.

E.g.

[katex] (4\times10^{5})\times(2\times10^{3}) = 8\times10^{8} [/katex].
The power of ten is [katex] 10^{8} [/katex], NOT [katex] 10^{15}. [/katex]

• Dividing the powers

When dividing numbers in standard form, a common mistake is dividing the powers rather than subtracting the powers.

E.g.

[katex] (8\times10^{9})\div(2\times10^{3}) = 4\times10^{6} [/katex].
The power of ten is [katex] 10^{6} [/katex], NOT [katex] 10^{3}. [/katex]

• Not converting solutions to standard form

After calculating with standard form, a common mistake is not checking that the first part of the number is 1 ≤ [katex] x[/katex] < 10.

E.g.

[katex] 45 [/katex] x [katex] 10^{6} [/katex] is not in standard form.

• Negative numbers

Not adding or subtracting negative powers correctly, especially when dividing by a negative power as here you would be subtracting a negative number which has the same effect as adding.

Multiplying and dividing standard form is part of our series of lessons to support revision on standard form. You may find it helpful to start with the main standard form lesson for a summary of what to expect, or use the step by step guides below for further detail on individual topics. Other lessons in this series include:

### Practice multiplying and dividing standard form questions

1. Work out [katex] (2\times10^{6})\times(3\times10^{4}) [/katex]. Write your answer in standard form.

[katex] 5 \times 10^{10} [/katex]

[katex] 6 \times 10^{10} [/katex]

[katex] 6 \times 10^{24} [/katex]

[katex] 5 \times 10^{24} [/katex]

[katex]2 \times 3 = 6[/katex]
[katex]10^{6} \times 10^{4} = 10^{10}[/katex]
[katex](2 \times 10^{6}) \times (3 \times 10^{4}) = 6 \times 10^{10}[/katex]

2. Work out [katex] (4\times10^{5})\times(7\times10^{6}) [/katex]. Write your answer in standard form.

[katex] 28 \times 10^{11} [/katex]

[katex] 2.8 \times 10^{11} [/katex]

[katex] 2.8 \times 10^{12} [/katex]

[katex] 0.28 \times 10^{13} [/katex]

[katex] 4 \times 7 = 28\\
10^{5} \times 10^{6} = 10^{11}\\
(4 \times 10^{5}) \times (7 \times 10^{6}) = 28 \times 10^{11} [/katex]

This answer is not in standard form because [katex] 28 [/katex] is not between [katex] 1 [/katex] and [katex] 10 [/katex]. We need to divide [katex] 28 [/katex] by [katex] 10 [/katex] and, to compensate, multiply [katex] 10^{11} [/katex] by [katex] 10 [/katex], increasing the power by [katex] 1 [/katex].

This gives us [katex] 2.8 \times 10^{12} [/katex]

3. Work out [katex] (6\times10^{8}) \div (3\times10^{5}) [/katex]. Write your answer in standard form.

[katex] 2 \times 10^{3} [/katex]

[katex] 2 \times 10^{1.6} [/katex]

[katex] 3 \times 10^{3} [/katex]

[katex] 0.2 \times 10^{4} [/katex]

[katex] 6 \div 3 = 2\\
10^{8} \div 10^{5} = 10^{3}\\
(6 \times 10^{8}) \div (3 \times 10^{5}) = 2 \times 10^{3} [/katex]

4. Work out [katex] (2\times10^{4})\div (8\times10^{-3}) [/katex]. Write your answer in standard form.

[katex] 4 \times 10^{7} [/katex]

[katex] 0.25 \times 10^{7} [/katex]

[katex] 2.5 \times 10^{6} [/katex]

[katex] 2.5 \times 10^{8} [/katex]

[katex] 2 \div 8 = 0.25\\
10^{4} \div 10^{-3} = 10^{7}\\
(2 \times 10^{4}) \div (8 \times 10^{-3}) = 0.25 \times 10^{7} [/katex]

This answer is not in standard form because [katex] 0.25 [/katex] is not between [katex] 1 [/katex] and [katex] 10 [/katex]. We need to multiply [katex] 0.25 [/katex] by [katex] 10 [/katex] and, to compensate, divide [katex] 10^{7} [/katex] by [katex] 10 [/katex], decreasing the power by [katex] 1 [/katex].

This gives us [katex] 2.5 \times 10^{6} [/katex]

5. Work out [katex] (5\times10^{3})^{2} [/katex]. Write your answer in standard form.

[katex] 25 \times 10^{6} [/katex]

[katex] 25 \times 10^{5} [/katex]

[katex] 1.0 \times 10^{7} [/katex]

[katex] 2.5 \times 10^{7} [/katex]

[katex] (5 \times 10^{3})^{2}=(5 \times 10^{3}) \times (5 \times 10^{3})\\
5 \times 5 = 25\\
10^{3} \times 10^{3}=10^{6}\\
(5 \times 10^{3})^{2}=25 \times 10^{6} [/katex]

This answer is not in standard form because [katex] 25 [/katex] is not between [katex] 1 [/katex] and [katex] 10 [/katex]. We need to divide [katex] 25 [/katex] by [katex] 10 [/katex] and, to compensate, multiply [katex] 10^{6} [/katex] by [katex] 10 [/katex], increasing the power by [katex] 1 [/katex].

This gives us [katex] 2.5 \times 10^{7} [/katex]

6. Work out [katex] (7\times10^{5})^{3} [/katex]. Write your answer in standard form.

[katex] 4.9 \times 10^{11} [/katex]

[katex] 3.43 \times 10^{17} [/katex]

[katex] 343 \times 10^{15} [/katex]

[katex] 3.43 \times 10^{127} [/katex]

[katex] (7 \times 10^{5})^{3}=(7 \times 10^{5}) \times (7 \times 10^{5}) \times (7 \times 10^{5})\\
7 \times 7 \times 7 = 343\\
10^{5} \times 10^{5} \times 10^{5} =10^{15}\\
(7 \times 10^{5})^{3}=343 \times 10^{15} [/katex]

This answer is not in standard form because [katex] 343 [/katex] is not between [katex] 1 [/katex] and [katex] 10 [/katex]. We need to divide [katex] 343 [/katex] by [katex] 100 [/katex] and, to compensate, multiply [katex] 10^{15} [/katex] by [katex] 100 [/katex], increasing the power by [katex] 2 [/katex].

This gives us [katex] 3.43 \times 10^{17} [/katex]

### Multiplying and dividing standard form GCSE questions

1. A cube has side lengths of [katex] 2\times10^{3} [/katex] metres. Calculate the surface area of the cube. Write your answer in standard form.

(3 marks)

Finding the area of one face: [katex] 4\times10^{6} [/katex]

(1)

Multiply by [katex] 6 [/katex] or correct answer not in standard form.

(1)

[katex] 2.4\times10^{7}m^{2} [/katex]

(1)

2. Work out [katex] \frac{9.3\times10^{8}}{3.1\times10^{2}} [/katex]. Give your answer in standard form.

(2 marks)

[katex] 9.3\div 3.1 = 3 [/katex] or [katex]10^{8} \div 10^{2} = 10^{6} [/katex]

(1)

[katex] 3\times10^{6} [/katex]

(1)

3.

a) Write [katex] 75000[/katex] in standard form.

b) Write [katex]0.03[/katex] in standard form.

c) Using your answers to a) and b), and also the formula [katex]F=ma[/katex], calculate the value of [katex]F[/katex] when [katex]m=75000[/katex] and [katex]a=0.03[/katex]. Write your answer in standard form.

(5 marks)

a) [katex]75000[/katex] in standard form is [katex]7.5 \times 10^{4}[/katex]

(1)

b) [katex]0.03[/katex] in standard form is [katex] 3 \times 10^{-2}[/katex]

(1)

c) [katex] F = ma [/katex]

Therefore,

[katex] F=7.5 \times 10^{4} \times 3 \times 10^{-2} [/katex]

(1)

[katex]7.5 \times 3 =22.5[/katex]

[katex]10^{4} \times 10^{-2} = 10^{2}[/katex]

(1)

[katex]22.5 \times 10^{2} = 2.25 \times 10^{3}[/katex]

[katex] F=2.25 \times 10^{3}[/katex]

(1)

## Learning checklist

You have now learned how to:

• Multiply numbers in standard form
• Divide numbers in standard form
• Square and cube numbers in standard form

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