Estimate sums, differences, products and quotients: word problems

Key notes :

1️⃣ What is Estimation?

• Estimation means finding a number close to the exact answer. 🔢
• We estimate to save time or check our answers. ⏱️
• Example: 47 + 32 ≈ 50 + 30 = 80 ✅

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2️⃣ Rounding for Estimation

To estimate, we often round numbers to the nearest:

• 10 (for smaller numbers)
• 100 (for bigger numbers)

Rounding helps make calculations easier. 🎯

Example: 76 → 80, 243 → 200

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3️⃣ Estimating Sums (Addition) ➕

Step 1: Round each number to a friendly number.

Step 2: Add the rounded numbers.

Example:

• Word problem: A shop sold 48 apples on Monday and 73 on Tuesday. About how many apples were sold in total?
• Estimate: 48 ≈ 50, 73 ≈ 70 → 50 + 70 = 120 apples

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4️⃣ Estimating Differences (Subtraction) ➖

Step 1: Round each number.

Step 2: Subtract the rounded numbers.

Example:

• Word problem: There were 256 books in the library. 129 books were borrowed. About how many books remain?
• Estimate: 256 ≈ 260, 129 ≈ 130 → 260 − 130 = 130 books

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5️⃣ Estimating Products (Multiplication) ✖️

Round numbers to easier numbers.

Multiply the rounded numbers to estimate.

Example:

• Word problem: A class has 28 students. Each student has 6 pencils. About how many pencils are there?
• Estimate: 28 ≈ 30, 6 → 6 → 30 × 6 = 180 pencils

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6️⃣ Estimating Quotients (Division) ➗

Round the dividend (number to be divided) and sometimes the divisor to friendly numbers.

Divide the rounded numbers to estimate.

Example:

• Word problem: 195 candies are to be shared among 9 children. About how many candies will each get?
• Estimate: 195 ≈ 200, 9 ≈ 10 → 200 ÷ 10 = 20 candies

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7️⃣ Tips for Word Problems 📝

• Read carefully: Understand what is being asked. 👀
• Identify operation: Decide whether it’s +, −, ×, ÷.
• Round numbers: Make them easier to work with.
• Write the estimated answer: Use it to check reasonableness. ✅

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8️⃣ Fun Example

• Word problem: A farmer has 47 cows and 36 goats. About how many animals does he have in total?
• Round: 47 → 50, 36 → 40
• Add: 50 + 40 = 90 animals 🐄🐐

Learn with an example

Let’s practice!🖊️