Codes: AC9M7N05. Goal: round decimals to a stated place and explain whether a context supports that precision. Prepare: place-value line and examples.
- Open · 2 min. Show
3.468 m. Ask: “If the measuring tape is reported to hundredths of a metre, what should we write?” - Model · 5 min. Mark hundredths in 3.468; the thousandths digit 8 rounds 6 hundredths up to 7. Write 3.47 m. Say the unrounded measurement would require an instrument that genuinely supports thousandths; our number is a practice example, not a measurement we took.
- Guided changes · 6 min. Round
18.374to one decimal → 18.4. Round0.946to two decimals → 0.95. Ask which place is kept and which next digit decides. - Context decisions · 7 min. Pairs get invented values: a relay time 14.387 s reported to hundredths → 14.39 s, and a jar mass 2.136 kg to tenths → 2.1 kg. Discuss why showing three decimal places from a rough estimate would imply false precision.
- Estimate check · 3 min. Ask whether 3.468 is closer to 3.46 or 3.47. It is 0.008 from 3.46 and 0.002 from 3.47, so the rounded result is sensible. Mark both hundredths on a line.
- Exit · 2 min. Everyone rounds
12.684to one decimal → 12.7 and names the hundredths digit 8 as the reason. Focus learners must state the requested place.
Access: enlarged place labels, tactile digit cards, spoken value plus accessible text. A learner may type the explanation; handwriting is not the rounding evidence.