Percentages (Leaving Cert Mathematics): Revision Notes

Calculating Percentage Error

1. Derive the observed value and the accurate value
2. Subtract the observed value from the accurate value and take the absolute value.
3. Divide the error by the accurate value.
4. Multiply by $100$ to calculate the percentage error.

Find the percentage error of taking $1$ cm as $0.8$ cm

Observed value = $1$ cm.

Accurate value = $0.8$ cm.

Error = $|0.8-1|=0.2$

Relative error = $\frac{0.2}{0.8}=\frac{1}{4}$

Percentage error = $0.25 \cdot 100=25\%$