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Lesson ⁦4-2⁩: Modeling and Writing Number Sentences

Math · Fourth Grade, Primary · Unit 4: Patterns and Algebra · First Semester

A 10-question quiz; after every question you'll see the right answer with an explanation.
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What will you learn in this lesson?

In this lesson we learn to turn word situations into number sentences with a symbol or a box for the unknown number, such as: Sarah had some pencils, got 6 more, and now has 15. This is an essential problem-solving skill.

  • Writes a number sentence that represents a word situation
  • Uses a symbol or a box to stand for the unknown number
  • Solves the number sentence to find the unknown
  • Writes a word problem that fits a given number sentence

💡 Tip: Turn words into symbols: "added," "increased," and "total" mean addition, while "spent," "left," "difference," and "less than" mean subtraction. Then put the unknown in place of what you don't know.

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Worked examples from the Modeling and Writing Number Sentences lesson questions

Which expression shows "5 more than 12"?
  • 12 + 5
  • 12 − 5
  • 5 − 12
  • 12 + 12
✓ 12 + 5
The words "more than" mean addition, so the expression is 12 + 5.
Which expression shows "8 less than 30"?
  • 30 − 8
  • 8 − 30
  • 30 + 8
  • 8 + 8
✓ 30 − 8
The words "less than" mean subtraction, so we subtract 8 from 30: the expression is 30 − 8.
Show more examples (3)
Khalid had 6 balls, then he bought 4 more balls, and now he has 10 balls. Which number sentence shows this?
  • 6 + 4 = 10
  • 10 + 4 = 14
  • 6 − 4 = 2
  • 6 + 10 = 16
✓ 6 + 4 = 10
He started with 6 balls, 4 were added, and the total is 10: the sentence is 6 + 4 = 10.
There are 28 students in the classroom. Some of them went to the lab, and 19 students stayed. Which number sentence shows the situation?
  • 28 − □ = 19
  • 28 + □ = 19
  • 19 − □ = 28
  • □ − 19 = 28
✓ 28 − □ = 19
The number of students at the start is 28, an unknown number (□) was subtracted from it, and 19 were left: the sentence is 28 − □ = 19.
In the sentence 28 − □ = 19, how many students went to the lab?
  • 9
  • 47
  • 11
  • 8
✓ 9
28 − 19 = 9, and we check: 28 − 9 = 19.

FAQ about the Modeling and Writing Number Sentences lesson

How do I write a number sentence for: Khalid had some riyals, spent 8, and has 12 left?

I use a box for the unknown: □ − 8 = 12, and the solution is □ = 12 + 8 = 20 riyals.

Why do we use a symbol for the unknown number?

Because the symbol holds the place of the number we don't know, so we can write the whole situation and then look for the number that makes the sentence true.

How do I study the lesson Modeling and Writing Number Sentences and test myself on it?

Start the lesson quiz on Study with Ghada: 10 questions from the Math Fourth Grade, Primary question bank. After each answer you'll see the right answer with an explanation, and any questions you miss move to “Review my mistakes” until you master them.

Are Study with Ghada quizzes free and aligned with the curriculum?

Yes, completely free. They're built on the Math - Grade 4 - Semester 1 lessons in the same order as the book, and every question is reviewed and approved by a teacher before students see it.

Unit 4 lessons: Patterns and Algebra

⁦4-1⁩ Expressions and Number Sentences ⁦4-3⁩ Problem-Solving Strategy: Logical Reasoning ⁦4-4⁩ Find a Rule from a Table ⁦4-5⁩ Function Tables: Addition and Subtraction Tables ⁦4-6⁩ Problem-Solving Investigation: Choose the Best Strategy ⁦4-7⁩ Function Tables: Multiplication and Division Tables All Math Fourth Grade, Primary lessons →
← ⁦4-1⁩ Expressions and Number Sentences ⁦4-3⁩ Problem-Solving Strategy: Logical Reasoning →