Reach for the Star

Rounding error intervals and bounds · Optional extension

L055 · Allow 10–15 minutes for learners ready to move on. Answers are available after an attempt.

Stretch

A rectangle is 8.2 cm by 5.6 cm to the nearest 0.1 cm. Find its lower area bound.

Reveal a worked check after attempting

8.15×5.55=45.2325 cm².

Deep challenge

A rounded length is 10 cm to nearest cm. Is 10.5 cm included? Explain.

Reveal a worked check after attempting

No; interval is 9.5≤L<10.5. 10.5 rounds to 11 under the standard convention.

Recall & Review: feedback and extension integration

Lesson L055: Rounding error intervals and bounds

Objective: Describe rounding intervals and reason about limits of accuracy.

60-minute structure: 0-7 Connect & Check; 7-14 Share; 14-25 Present/model; 25-44 Apply route choice/practice; 44-52 independent exam-style check; 52-60 Recall & Review, WWW/EBI and next step.

What Went Well (WWW)

I selected an efficient numerical method, showed the key steps clearly and checked the sign, size or accuracy of my answer.

Even Better If (EBI)

I will make the place-value, sign or operation decision explicit and use estimation or an inverse calculation to check a fresh question.

Stretch and deep challenge

Stretch: A rectangle is 8.2 cm by 5.6 cm to the nearest 0.1 cm. Find its lower area bound.

Deep challenge: A rounded length is 10 cm to nearest cm. Is 10.5 cm included? Explain.