Rounding Off — Revision Notes

⚡ 30-Second Revision

Identify decimal places versus significant figures.
Preserve intermediate precision.
Round the final result once.
Rounded inputs represent intervals.
Tighten estimates when options or thresholds are close.

2-Minute Revision

Rounding requires a specified place and convention. Direct rounding can differ from repeated rounding, so retain original digits until the final step. A value rounded to the nearest unit represents an interval of possible originals. Use estimation when its error is small enough for the decision, and calculate more precisely when it is not. Report no more precision than the task and inputs justify.

5-Minute Revision

Round 6.249 directly to one decimal place: 6.2. Now round to two decimal places first: 6.25, which becomes 6.3 at one decimal place under half-up rounding. Explain the discrepancy. Next, if a positive length is reported as 24 cm to the nearest centimetre, its original value lies in [23.5, 24.5) cm. A claim that it exceeds 24.2 cm cannot be decided from that rounded report alone. Give one possible value below and one above the threshold.

Vyyuha Quick Recall

Place → Preserve → Round → Bound. Keep digits until the precision decision is clear.