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Study with Ghada› Math Fourth Grade, Primary› Unit 2

Lesson ⁦2-3⁩: Problem-Solving Skill: Estimate or Find an Exact Answer

Math · Fourth Grade, Primary · Unit 2: Addition and Subtraction · 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?

This lesson teaches you when you need an exact answer and when an estimate is enough, using words in the problem such as "about" and "is it enough." Then you solve the problem with the four steps.

  • Determines from the wording whether the problem asks for an estimate or an exact answer
  • Solves the problem using the steps Understand, Plan, Solve, and Check
  • Uses estimation in situations that don't require precision
  • Checks an exact answer by comparing it with an estimate

💡 Tip: Look in the problem for words like "about," "approximately," and "is it enough"; they show that an estimate is enough. "Exactly how many" needs an exact calculation.

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Worked examples from the Problem-Solving Skill: Estimate or Find an Exact Answer lesson questions

Which of the following situations needs an exact answer?
  • Calculating the change the seller gives back to the buyer
  • Knowing the approximate population of a neighborhood
  • Knowing whether the money is roughly enough to buy the items
  • Guessing the number of people at the school party
✓ Calculating the change the seller gives back to the buyer
The seller must give back exactly the right amount, so we need an exact answer, not an estimate.
Which word in a word problem usually shows that an estimate is enough?
  • About
  • Exactly
  • Precisely
  • Specifically
✓ About
The word "about" or "approximately" means an estimated answer is enough, while "exactly" asks for an exact answer.
Show more examples (3)
In which of the following situations is an estimate enough?
  • Knowing the approximate number of visitors to a park on a holiday
  • Calculating the change from the cost of the items
  • Writing a phone number
  • Calculating a student's total score on a test
✓ Knowing the approximate number of visitors to a park on a holiday
The approximate number of visitors does not need to be exact, while change, test scores, and phone numbers need exact numbers.
Aisha has 100 riyals and wants to buy a bag for 48 riyals and shoes for 39 riyals. Is her money enough?
  • Yes, because 50 + 40 = 90, which is less than 100
  • No, because 48 + 39 is greater than 100
  • No, because 50 + 40 = 110
  • Yes, because 48 − 39 = 9
✓ Yes, because 50 + 40 = 90, which is less than 100
We rounded both prices up (50 and 40), and their sum, 90, is less than 100, so the money is definitely enough. The exact total is 87 riyals.
Faisal's mother bought items for 237 riyals and paid 500 riyals. What do we need to find the change, and how much is it?
  • An exact answer: 263 riyals
  • An estimate: about 300 riyals
  • An exact answer: 273 riyals
  • An exact answer: 737 riyals
✓ An exact answer: 263 riyals
The change must be exact: 500 − 237 = 263 riyals. Check: 263 + 237 = 500.

FAQ about the Problem-Solving Skill: Estimate or Find an Exact Answer lesson

When is an estimate enough to solve a problem?

It is enough when the question asks for an approximate value or a decision like whether there is enough money. If Ahmed has 100 riyals and wants to buy items for 38 and 41 riyals, the estimate 40 + 40 = 80 is enough to know he has enough money.

When do I need an exact answer?

When the exact number is asked for, such as the change left after a purchase or exactly how many seats are needed.

How do I study the lesson Problem-Solving Skill: Estimate or Find an Exact Answer 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 2 lessons: Addition and Subtraction

⁦2-1⁩ Algebra: Addition Properties and Subtraction Rules ⁦2-2⁩ Estimate Sums and Differences ⁦2-4⁩ Addition ⁦2-5⁩ Subtraction ⁦2-6⁩ Subtraction with Zeros All Math Fourth Grade, Primary lessons →
← ⁦2-2⁩ Estimate Sums and Differences ⁦2-4⁩ Addition →