Mathematics
Grade 4
15 min
Estimate sums, differences, products, and quotients: word problems
Estimate sums, differences, products, and quotients: word problems
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Introduction & Learning Objectives
Learning Objectives
Identify the correct operation (addition, subtraction, multiplication, or division) required by a word problem.
Round multi-digit numbers to a suitable place value (e.g., nearest ten, hundred) to simplify calculations.
Calculate an estimated sum, difference, product, or quotient to solve a word problem.
Use clue words like 'about,' 'approximately,' or 'estimate' to know when an exact answer is not needed.
Use compatible numbers as an alternative strategy for estimating products and quotients.
Explain why an estimated answer is a reasonable solution to a word problem.
Imagine you have $20 and want to buy 3 toys that cost $7.95 each. Do you have enough money? 🧸 Let's learn the math superpower of estimating to find out fas...
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Key Concepts & Vocabulary
TermDefinitionExample
EstimateTo find a number that is close to the exact answer. It is not a wild guess, but a careful approximation.To estimate 29 + 52, you could calculate 30 + 50 = 80.
RoundingA way of making a number simpler by changing it to the nearest ten, hundred, or other place value.The number 18 can be rounded to 20. The number 123 can be rounded to 120 (nearest ten) or 100 (nearest hundred).
SumThe result of adding two or more numbers together.The sum of 8 and 5 is 13.
DifferenceThe result of subtracting one number from another.The difference between 10 and 4 is 6.
ProductThe result of multiplying two or more numbers together.The product of 7 and 3 is 21.
QuotientThe result of dividing one number by another.The quotient of 15 divided by 3 is 5.
Compatible NumbersNumbers that...
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Core Formulas
The Rounding Rule
1. Find the place you are rounding to. 2. Look at the digit to its right. 3. If the digit is 5 or more, round up. 4. If the digit is 4 or less, keep it the same.
Use this rule to change the numbers in a word problem into simpler numbers before you calculate. For example, to round 378 to the nearest hundred, look at the 7. Since it's 5 or more, the 3 rounds up to 4, making it 400.
The Estimation Word Problem Strategy
Read \rightarrow Round \rightarrow Calculate \rightarrow Answer
This is the four-step process for solving estimation word problems. First, read and understand the problem. Second, round the numbers to make them easy to work with. Third, perform the calculation (+, -, x, /). Finally, write your answer in a sentence.
5 more steps in this tutorial
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Challenging
A student estimates that 492 + 307 is about 800. Why is this a reasonable estimate?
A.Because the exact answer is 799, which is very close to 800.
B.Because 400 + 300 = 700, which is a close number.
C.Because you can round 492 to 500 and 307 to 300, and their sum is 800.
D.Because you should always round both numbers down.
Challenging
A rectangular garden is 28 feet wide and 63 feet long. The gardener wants to put a fence around it. About how many feet of fencing will she need?
A.180 feet
B.90 feet
C.1,800 feet
D.182 feet
Challenging
A school needs to buy 38 new laptops, and each one costs $489. The school has a budget of $20,000. Which of the following is the most accurate estimate and conclusion?
A.40 x $400 = $16,000. The school has enough money.
B.30 x $500 = $15,000. The school has enough money.
C.40 x $500 = $20,000. The school has just enough money.
D.The exact cost is $18,582, so they have enough money.
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