Unless a question says otherwise: round final numeric answers to 3 significant figures, and round final angles to 1 decimal place.

Extended papers often chain several operations — roots, powers, trig — into one expression. Rounding an intermediate result before the calculation is finished silently corrupts the last significant figure of your final answer, even though the working "looks" fine.

Use your calculator's memory or ANS key to store an unrounded result the moment you calculate it, then recall that stored value in the next step instead of retyping a rounded version.

Worked Example

Evaluate $x = \dfrac{\sqrt{18.4^2 - 7.9}}{5.3 \times 2.1 - 1.6}$, giving your answer correct to $3$ significant figures.

1. Numerator: $18.4^2 - 7.9 = 338.56 - 7.9 = 330.66$, so $\sqrt{330.66} = 18.1839\ldots$ — keep the full calculator display, don't round yet.
2. Denominator: $5.3\times2.1 - 1.6 = 11.13-1.6 = 9.53$.
3. Divide using the stored, unrounded numerator: $18.1839\ldots \div 9.53 = 1.90807\ldots$
4. Round only now, to $3$ significant figures: $1.91$.

If you had rounded the numerator to $18.18$ before dividing, you'd get a different — and wrong — final significant figure.

A calculator has no idea what your answer represents, so decimals need translating back into the right units by hand.

• Money: a display of $4.8$ in a money context means \4.80$, not$\$4.8$ — always pad to $2$ decimal places for currency.
• Time: a display of $2.5$ representing hours means $2$ hours $30$ minutes, not $2$ hours $50$ minutes — the decimal part is a fraction of $60$ minutes, not a direct minute count. Similarly, $3.25$ hours means $3$ hours $15$ minutes ($0.25\times60=15$).

Worked Example

A journey takes $2.75$ hours. Express this as hours and minutes.

1. The whole-number part is the hours: $2$ hours.
2. Convert the decimal part to minutes by multiplying by $60$: $0.75\times60=45$.
3. The journey takes $2$ hours $45$ minutes.

Always confirm the calculator is set to degrees (usually shown as a small "D" or "DEG" in the display) before evaluating any sine, cosine, or tangent value, since IGCSE angle questions are always given in degrees. A calculator left in radian mode will produce numerically plausible-looking but completely wrong answers, with no obvious warning sign in the output itself.