Calculator and number skills Revision Notes for Edexcel GCSE Maths

Calculator and number skills

Essential calculator functions

Understanding your calculator is crucial for GCSE maths success. Here are the most important keys you need to know:

Basic function keys

x² - Squares a number (multiplies it by itself)
x³ - Cubes a number (multiplies it by itself three times)
x⁻¹ - Finds the reciprocal of a number (1 divided by the number)
(-) - Enters negative numbers
√ - Calculates the square root of a number
∛ - Calculates the cube root of a number (you may need to press shift first)
Ans - Uses your previous answer in a new calculation
S⇔D - Converts between fractions/surds and decimals (not available on all calculators)

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Familiarise yourself with your specific calculator model, as key locations and functions may vary between different brands and models. Practice using these functions regularly to build confidence.

Order of operations - BIDMAS

When performing calculations, you must follow the correct sequence. Remember BIDMAS:

**B**rackets - Work out brackets first
**I**ndices - Then powers and roots
**D**ivision - Then division
**M**ultiplication - Then multiplication
**A**ddition - Then addition
**S**ubtraction - Finally subtraction

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Worked Example: BIDMAS in Action

For the calculation $(10 - 7) + 4 × 3²$ :

Step 1: Brackets first: $(10 - 7) = 3$ Step 2: Indices next: $3² = 9$ Step 3: Multiplication: $4 × 9 = 36$ Step 4: Addition last: $3 + 36 = 39$

Final answer: $39$

Understanding reciprocals

Reciprocal - The reciprocal of a number is found by dividing 1 by that number.

Finding reciprocals

To find a reciprocal, write the number as a fraction and flip it upside down:

The reciprocal of $7$ is $\frac{1}{7}$ (since $7 = \frac{7}{1}$ , flip to get $\frac{1}{7}$ )
The reciprocal of $\frac{3}{4}$ is $\frac{4}{3}$ (flip the fraction)

You can use the x⁻¹ key on your calculator to find reciprocals quickly.

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Remember that multiplying a number by its reciprocal always gives 1. For example: $7 × \frac{1}{7} = 1$ and $\frac{3}{4} × \frac{4}{3} = 1$ .

Calculator techniques for exams

Working with complex calculations

When faced with calculations like $\frac{\sqrt{8.3}}{12.5 - 7.3}$ :

Write down all numbers from your calculator display - don't round too early
Work out the numerator and denominator separately before dividing
Read the question carefully - check if you need a decimal answer
Use the S⇔D button if available to convert between fractions and decimals

Checking your answers

Always verify your calculator work by:

Re-entering the calculation using the reciprocal key for division problems
Estimating whether your answer seems reasonable
Reading all figures from your calculator display as instructed

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Critical Exam Technique: Never round intermediate results during multi-step calculations. Only round your final answer according to the question's requirements. Early rounding can lead to significant errors that will cost you marks.

Common exam mistakes to avoid

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Avoid These Common Pitfalls:

Not following BIDMAS when working without a calculator
Rounding too early in multi-step calculations
Forgetting to convert fraction answers to decimals when required
Not showing working clearly on your calculator display
Misreading calculator displays - write down all the digits shown

Practice problems

Without calculator (use BIDMAS):

Work out $10 - 3 × 2$
Calculate $84 ÷ (6 + 6)$
Find the value of $8 + 3²$
Work out $(9 - 4)³$

With calculator:

Calculate $\sqrt{244} + 717$
Work out $\sqrt[3]{3.1} - 0.356$

Remember to give decimal answers where specified and show all working clearly.

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Key Points to Remember:

Know your calculator keys - practice using square, cube, reciprocal and root functions
Always use BIDMAS for order of operations - Brackets, Indices, Division, Multiplication, Addition, Subtraction
Reciprocals flip fractions - the reciprocal of $\frac{a}{b}$ is $\frac{b}{a}$
Write down all calculator digits before rounding to avoid errors
Check your answers by re-calculating or estimating to spot mistakes

Calculator and number skills (Edexcel GCSE Maths): Revision Notes