When to estimate
| If the options | Then |
|---|---|
| Differ by an order of magnitude | Estimate — exact work is wasted |
| Differ by a factor of two or more | Estimate first, compute only if two survive |
| Differ in the last digit | Compute exactly |
| Are algebraic expressions | Substitute a convenient number instead |
Reading the options before starting the calculation is what makes this possible, and it is the step most candidates skip.
Estimating without drifting
- Round in opposite directions where you can, so the errors partly cancel.
- Keep track of whether your estimate is above or below the true value.
- Round to one significant figure first; add precision only if needed.
- For percentages, use 10% as the unit and scale.
If two options survive your estimate, you have still eliminated three — which turns a five-way choice into a coin toss you can usually settle with one more step.
Estimation — FAQs
2 questions
When the options differ only in their last digits. Then exact arithmetic is required.
Round in opposite directions where possible and track whether you are above or below.
More mathematical equations question types
Sources
Written from the test board's own published material and checked on 1 October 2026.