Open Sentences Basic 2 Mathematics Lesson Note

Learning Objectives

By the end of this week, pupils should be able to:

• Count and identify numbers from 1-600 (focus on 570-600)
• Order numbers from 1-600
• Write numbers 570-600 in numerals and words
• Identify an open sentence
• Determine when to add or subtract in an open sentence
• Solve open sentences by performing arithmetic operations

Lesson Content

Day 1: Counting to 600

New Milestone – 600!

• Practice counting from 1-600
• Focus on numbers 570-600: 570, 571, 572… 600
• Special attention to reaching 600: 598, 599, 600
• Learn to read: “six hundred”

Number Writing:

• Practice writing 570, 580, 590, 600
• Write in both numerals and words
• Celebrate reaching 600!

Day 2-3: Understanding Open Sentences

What is an Open Sentence? An open sentence is a math sentence with a missing number, shown by a box □ or blank ___.

Examples of Open Sentences:

• 5 + □ = 8
• 12 – ___ = 7
• ___ + 6 = 15
• 20 – □ = 13

What is a Complete Sentence?

• 5 + 3 = 8 ✓ (This is complete)
• 12 – 5 = 7 ✓ (This is complete)

Day 3-4: Solving Open Sentences

How to Solve Open Sentences:

Type 1: Addition Open Sentences

• 7 + □ = 12
• Think: “7 plus what equals 12?”
• Count up from 7: 8, 9, 10, 11, 12 (that’s 5 steps)
• Or think: 12 – 7 = 5
• Answer: □ = 5

Type 2: Subtraction Open Sentences

• 15 – □ = 9
• Think: “15 minus what equals 9?”
• Think: 15 – 9 = 6
• Answer: □ = 6

Type 3: Missing First Number

• □ + 8 = 15
• Think: “What plus 8 equals 15?”
• Think: 15 – 8 = 7
• Answer: □ = 7

Day 5: When to Add or Subtract

Clues for Addition:

• Words like: altogether, total, sum, plus, more
• When things are put together
• When we want to find the whole

Clues for Subtraction:

• Words like: left, remaining, difference, take away, less
• When things are removed
• When we want to find what’s left

Decision Making: Look at the open sentence and think:

• “Are we putting together or taking away?”
• “Do we need the total or what’s left?”

Examples in Class

Open Sentence Examples:

Example 1: 23 + □ = 45

• Think: “23 plus what equals 45?”
• Solution: 45 – 23 = 22
• Answer: □ = 22

Example 2: 67 – □ = 34

• Think: “67 minus what equals 34?”
• Solution: 67 – 34 = 33
• Answer: □ = 33

Example 3: □ + 28 = 56

• Think: “What plus 28 equals 56?”
• Solution: 56 – 28 = 28
• Answer: □ = 28

Real-Life Open Sentences:

Shopping Example: “Mom bought bread for 25 naira and something else. She spent 67 naira altogether. How much did the other item cost?” 25 + □ = 67 □ = 67 – 25 = 42 naira

School Example: “There were some pupils in the hall. 23 pupils left, and 45 pupils remained. How many pupils were there originally?” □ – 23 = 45 □ = 45 + 23 = 68 pupils

Exercises

Exercise 1: Number Practice

Write these numbers:

1. Five hundred and seventy-five = ___
2. Five hundred and ninety-eight = ___
3. 583 in words = ___
4. 596 in words = ___

Order these numbers from smallest to largest: 5. 587, 592, 578, 600, 565

Exercise 2: Identifying Open Sentences

Circle the open sentences:

1. 8 + 5 = 13
2. 12 + □ = 20
3. 15 – 7 = 8
4. □ – 6 = 14
5. 9 + 4 = 13

Exercise 3: Simple Open Sentences

Solve these open sentences:

1. 5 + □ = 12, so □ = ___
2. 8 + □ = 15, so □ = ___
3. 6 + □ = 14, so □ = ___
4. 9 + □ = 17, so □ = ___

Exercise 4: Subtraction Open Sentences

Solve these:

1. 15 – □ = 8, so □ = ___
2. 20 – □ = 12, so □ = ___
3. 18 – □ = 9, so □ = ___
4. 25 – □ = 16, so □ = ___

Exercise 5: Missing First Number

Find the missing number:

1. □ + 7 = 15, so □ = ___
2. □ + 12 = 20, so □ = ___
3. □ – 8 = 14, so □ = ___
4. □ – 9 = 16, so □ = ___

Exercise 6: 2-Digit Open Sentences

Solve these larger open sentences:

1. 34 + □ = 67, so □ = ___
2. 56 – □ = 28, so □ = ___
3. □ + 29 = 78, so □ = ___
4. □ – 35 = 42, so □ = ___

Exercise 7: Word Problems as Open Sentences

Write and solve the open sentence:

1. Tom has 45 marbles. His friend gives him some more marbles. Now he has 73 marbles. How many marbles did his friend give him? Open sentence: 45 + □ = 73 Answer: □ = ___ 
2. Mary had some stickers. She gave 28 stickers to her sister. She has 34 stickers left. How many stickers did she have originally? Open sentence: □ – 28 = 34 Answer: □ = ___ 
3. A shop had 89 bottles. Some bottles were sold. 46 bottles remain. How many bottles were sold? Open sentence: 89 – □ = 46 Answer: □ = ___ 

Exercise 8: Mixed Practice

1. Should we add or subtract to solve: 23 + □ = 56?
2. Should we add or subtract to solve: 78 – □ = 34?
3. Create your own open sentence using addition.
4. Create your own open sentence using subtraction.

Fun Activities

• Missing Number Detective: Solve open sentence mysteries
• Balance Scale: Use a balance to show equality in equations
• Open Sentence Stories: Create word problems with missing numbers
• Math Puzzles: Fill in missing numbers in number patterns

Homework

• Practice solving 10 open sentences daily
• Create 3 open sentences using situations at home
• Practice writing numbers 570-600
• Look for “missing number” situations in daily life

Assessment

• Can the child count to 600 accurately?
• Do they understand what an open sentence is?
• Can they solve different types of open sentences?
• Can they decide whether to add or subtract?
• Can they create their own open sentences?
• Can they solve word problems using open sentences?