Parent guide · Grade 2 Math · Unit 4

Lesson 4.4 Checking with Addition

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 20–25 minutes
Goal: Check a subtraction by adding.
You need: Dice
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: “53 − 30” Listen for: 23
- Ask: “55 − 30” Listen for: 25
- Ask: “37 − 20” Listen for: 17
- Ask: “93 − 20” Listen for: 73
- Ask: “78 − 40” Listen for: 38
Teach the new idea
Say this: “If 63 − 28 = 35, then 35 + 28 should equal 63.”
Say this: “Always check: addition undoes subtraction.”
Say this: “Check: make sure an answer is right.”
Show how
Show: Find the missing number: 47 + ___ = 96
Say this: “Think: what goes with 47 to make 96?”
Say this: “96 − 47 = 49”
Say this: “Check: 47 + 49 = 96”
Answer: 49
Show: The oak is 87 feet tall. The apple tree is 26 feet tall. How much taller is the oak?
$comparison bar model$
Say this: “Unknown: the difference.”
Say this: “Bar model: a long bar of 87 and a short bar of 26; the difference is unknown.”
Say this: “Equation: 87 − 26 = ?”
Say this: “87 − 26 = 61”
Say this: “Answer: The oak is 61 feet taller.”
Answer: 61 feet. The oak is 61 feet taller.
Practice together
Do this: Your child does these with you. Let them try first; help only after a real try.
Ask: 69 − 32 = ___
Listen for: 37
If stuck: Ones: 9 − 2 = 7
Ask: 45 − 45 = ___
Listen for: 0
If stuck: Ones: 5 − 5 = 0
Ask: 85 − 54 = ___
Listen for: 31
If stuck: Ones: 5 − 4 = 1
7 more practice items on the lesson page, and on Worksheet A and Worksheet B.
Watch for
- Adding the wrong two numbers to check.
Game: Snakes and Subtraction
Start at 99. Roll two dice, make a two-digit number and subtract it. Check your partner’s answer by adding. First to go below 10 wins.
Narration
Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”
Listen for: Check a subtraction by adding.
Daily habit
One-minute subtraction drill on Fridays. Mental math: take 10 or 20 away from any two-digit number.

Spread over the week

5 sessions of 20–25 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.