Choose Useful Estimates

Overview

This is Lesson 9 of 18 in the unit Math in Our World. Students build on place-value understanding to decide whether rounding to the nearest ten or nearest hundred will produce a useful estimate. They compare exact and rounded prices or quantities, then explain whether their estimates are reasonable in everyday situations.

Learning intentions

Students will be able to:

• Identify whether the nearest ten or nearest hundred is more useful for a situation.
• Round a whole number to the selected place.
• Use an estimate to make a quick decision.
• Explain why an estimate is reasonable.
• Use the words estimate, exact, reasonable, nearest ten, and nearest hundred.

Success criteria

• I can choose whether to round to the nearest ten or nearest hundred.
• I can round a number correctly to the place I chose.
• I can explain why my estimate is useful and reasonable.
• I can compare an estimate with the exact amount.

Curriculum links

• Grade 3 Number and Operations — use place-value understanding to round whole numbers and reason about the size of numbers.
• Grade 3 Measurement and Data — estimate quantities and use addition or subtraction to solve one-step problems involving quantities in the same units.
• Grade 3 Operations and Algebraic Thinking — identify and explain arithmetic patterns using place-value and operation reasoning.

Lesson structure (30 minutes)

1. 0–3 min · Hook and learning goal. Open with the hook and learning-goal slides showing a shopping cart with exact prices of $47 and $52 beside rounded prices of $50 and $50; ask, “Would exact prices or estimates help you decide quickly if you have $100?” Students turn and talk, then share what they notice. State: “Today we will choose a useful estimate, not just round automatically.”

2. 3–15 min · Mini-lesson: I do. Use the exact-and-estimated-price examples to model the vocabulary and think aloud: “The exact total is $99. Rounding $47 and $52 to the nearest ten gives $50 + $50 = $100, which is useful for checking whether I have enough money.” Model a second example with a larger quantity, such as 286 books: nearest ten gives 290, while nearest hundred gives 300; explain that the best choice depends on the question. Students show a ten card or hundred card, identify the rounding place, and help decide whether each estimate is reasonable.

3. 15–20 min · Guided practice: We do. Display four picture-based situations in the guided matching prompts: shopping prices, classroom supplies, a collection of objects, and a larger quantity. Give each student a “ten” card and a “hundred” card. Read each short situation aloud, and ask students to hold up the card for the more useful place, round the number orally, and complete the sentence: “I chose the nearest ___ because ___.” Discuss different choices when both estimates are reasonable.

4. 20–26 min · Independent practice: You do. Distribute the four visual estimation tasks and five-question assessment. Students solve four visual tasks by circling nearest ten or nearest hundred, rounding, and selecting or writing whether the estimate is reasonable. Then they complete five three-choice assessment questions, each asking them to select a useful rounding place or estimate. Teacher conferences briefly with each student and records whether the student can choose, round, and justify.

5. 26–30 min · Review and exit check. Return to the final review and exit prompt and display: “A store has 398 pencils. Is 400 or 400? Which rounding place would you choose, and why?” Clarify that students must name the place, not only give an answer. Students share one response with a partner, then hand in the completed assessment. Ask two students to explain how a useful estimate can be different from an exact answer.

Resources

• the complete Choose a Useful Estimate slide deck
• the four visual estimation tasks and five-question assessment
• Teacher-made “nearest ten” and “nearest hundred” cards
• Large place-value chart
• Picture cards or projected shopping and quantity contexts
• Pencils and colored pencils
• Whiteboard and markers
• Optional calculator for checking exact totals
• Teacher observation checklist

Assessment

• During the mini-lesson and guided practice, listen for correct use of “nearest ten,” “nearest hundred,” “estimate,” and “reasonable.” Ask, “Why is that place useful?”
• Use the worksheet to check four visual estimation tasks and the five three-choice assessment questions. Look separately for choosing the place, rounding accurately, and explaining reasonableness.
• For a quick individual check, ask each student to round 264 to the nearest ten and nearest hundred, then explain which estimate would be more useful for deciding whether approximately 260 people can fit in a room.

Differentiation

• Support students with picture-based contexts, large numerals, a place-value chart, color-coded digits, and teacher-recorded directions. Read every prompt aloud and provide one example before independent work.
• Offer sentence frames: “I chose the nearest ___ because the situation asks about ___.” and “My estimate is reasonable because ___.”
• Provide reduced choices by showing only two possible rounding places or two possible estimates. Allow calculator checking after students make and explain their own estimate.
• For dyslexic students and students with reading difficulties, use icons, short captions, generous spacing, a clear sans-serif font, large numerals, and minimal written text. Accept oral explanations, pointing, or dictated responses.
• Challenge students to explain two strategies: for example, round each number first or find an approximate total after combining numbers. Ask which strategy is more efficient and why.