Parent guide · Grade 3 Math · Unit 1

Lesson 1.3 Estimating Sums

Written for the parent. Read the Say this lines aloud as they are, or in your own words. Answers for you are marked Listen for.

At a glance

Time: 5 sessions of 25–30 minutes
Goal: Estimate sums by rounding. Use an estimate to check an answer.
You need: Pencil and crayons
Print: Worksheet A · Worksheet B · the lesson page

Steps

Warm-up
Do this: Ask these out loud. Your child answers out loud; no paper needed.
- Ask: “5 + 2” Listen for: 7
- Ask: “7 + 2” Listen for: 9
- Ask: “8 + 4” Listen for: 12
- Ask: “7 + 4” Listen for: 11
Teach the new idea
Say this: “Round each number, then add the rounded numbers.”
Say this: “After working a problem exactly, compare with the estimate. If they are far apart, check again.”
Say this: “Estimate: a close answer, found quickly.”
Say this: “About: a word that asks for an estimate.”
Show how
Show: 404 + 106 = ___
Say this: “Ones: 4 + 6 = 10. Write 0 and regroup 1 to the tens.”
Say this: “Tens: 1 + 0 + 0 = 1. Write 1.”
Say this: “Hundreds: 4 + 1 = 5. Write 5.”
Say this: “404 + 106 = 510”
Answer: 510
Show: A carpenter cut 256 boards on Monday and 138 boards on Tuesday. How many boards did he cut?
$bar model$
Say this: “Unknown: the total.”
Say this: “Bar model: two parts, 256 and 138; the whole is unknown.”
Say this: “Equation: 256 + 138 = ?”
Say this: “256 + 138 = 394”
Say this: “Answer: He cut 394 boards.”
Answer: 394 boards. He cut 394 boards.
Practice together
Do this: Your child does these with you. Let them try first; help only after a real try.
Ask: Round 117 to the nearest 100.
Listen for: 100
If stuck: 117 is between 100 and 200.
Ask: Round 258 to the nearest 100.
Listen for: 300
If stuck: 258 is between 200 and 300.
Ask: Round 687 to the nearest 100.
Listen for: 700
If stuck: 687 is between 600 and 700.
7 more practice items on the lesson page, and on Worksheet A and Worksheet B.
Watch for
- Rounding the answer instead of the numbers.
Game: Round-Off
Draw a card with a 3-digit number. Both players say it rounded to the nearest 10 and the nearest 100. First correct answer scores.
Narration
Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”
Listen for: Estimate sums by rounding.; Use an estimate to check an answer.
Daily habit
Count by 10s and 100s across a thousand (980, 990, 1,000, 1,010). Addition facts drill twice a week.

Spread over the week

5 sessions of 25–30 minutes. Stop while it is still going well.

Session 1. Warm-up, then teach the new idea (steps 1 and 2).
Session 2. Warm-up again, then show how with the examples.
Session 3. Practice together, then play the game.
Session 4. More practice on the worksheet, and the daily habit.
Session 5. Quick check: narration and a few practice items. Move on when it is mostly right.