Using a CalculatorCambridge IGCSE Maths: Revision notes

Section 1

Why does calculator technique matter in exams?

A calculator only gives a correct final answer if it is used correctly. Examiners award marks for correct method AND correct use of the calculator — a wrong technique can lose marks even when the working is right.

The golden rule: avoid rounding intermediate values. Round only your FINAL answer, using either the full calculator display or the memory/ANS function throughout the calculation.

Key termsintermediate value

Common mistake

Rounding a value halfway through a calculation and then continuing with the rounded figure causes the final answer to drift away from the true value — this is heavily penalised in mark schemes.

Section 2

How do I enter time and angle values correctly?

Time and angles are not decimal by nature, so they must be entered carefully:

2 hours 30 minutes should be entered as 2.5 hours (30 minutes = 0.5 of an hour), not 2.30
An angle of 2 degrees 30 minutes 0 seconds is written as $2° \, 30' \, 0''$ and should be entered using the calculator's DMS (degrees/minutes/seconds) function, or converted to a decimal degree (2.5°)

Key termsDMS

Example

3 hours 45 minutes as a decimal = 3 + 45/60 = 3.75 hours.

Section 3

How do I interpret the calculator display correctly?

The calculator does not know the context of your problem, so you must interpret the number sensibly:

In a money context, a display of 4.8 means $4.80, not$ 4.08 or $4.8 in cents
In a time context, a display of 3.25 means 3 hours 15 minutes (0.25 x 60 = 15 minutes), NOT 3 hours 25 minutes
Always convert calculator decimals back into the correct real-world units before writing your final answer

Exam tip

When a mark scheme asks for an answer 'in context', always convert any decimal time or money display into the correctly formatted real-world value.

Section 4

What calculator settings and values do I need to know?

Use the calculator's built-in value of $\pi$ , or 3.142 if instructed, for accurate answers unless told to use an approximation
Make sure the calculator is in the correct angle mode (degrees, not radians) before trigonometry questions
Use brackets to force the correct order of operations, especially around numerators/denominators of fractions and powers

Must Know

Never round intermediate values — round only the final answer
Enter 2 hours 30 minutes as 2.5, not 2.30, when working in decimal hours
A calculator display of 4.8 in a money context means $4.80
A calculator display of 3.25 in a time context means 3 hours 15 minutes
Use π from the calculator, or 3.142 if specifically told to
Use brackets to control order of operations accurately

That's the notes covered.

Carry on to the next subtopic.