What you need to know
Strong number skills reduce errors across the whole 4MA1 course. Work accurately with fractions, percentages, standard form and bounds before reaching for a calculator, and keep track of exact values until rounding is requested.
- Convert confidently between fractions, decimals and percentages.
- Use standard form for very large or very small values.
- Apply percentage change with a multiplier.
- Use upper and lower bounds when measurements have been rounded.
Key mathematics
Percentage multiplier
\text{new value}=\text{original value}\times\left(1\pm\frac p{100}\right)
Use plus for increase and minus for decrease.Standard form
a\times10^n,\quad 1\le |a|<10
Keep one non-zero digit before the decimal point.Worked example
A 15% increase on 240 can be calculated using the multiplier $1.15$: $$240\times1.15=276.$$ This is safer than finding 15% separately when several percentage changes are involved.
EXAM TECHNIQUE
Exam tips
- Write the multiplier before using the calculator for percentage change.
- Do not round intermediate values unless the question tells you to.
- For bounds, identify the rounding unit first.
WATCH OUT
Common mistakes
- Applying a 15% decrease by multiplying by 0.15 instead of 0.85.
- Writing standard form with a coefficient greater than or equal to 10.
- Using rounded intermediate values and losing final accuracy.
Frequently asked questions
Why are number skills so important in IGCSE maths?
They appear inside algebra, geometry, statistics and real-world problems, so small number errors can cost marks across many topics.
When should I round?
Normally at the end, unless the question explicitly instructs you to round at an earlier stage.
What is the safest percentage-change method?
Use a multiplier such as 1.12 for a 12 percent increase or 0.88 for a 12 percent decrease.