Estimate sums and differences of decimals
key notes :
What is Estimation? 🤔
Estimation means finding a close or approximate value instead of the exact answer.
Helps to check your work quickly and make calculations easier. ✔️
Why Estimate Decimals? 💡
To save time when exact calculation is not needed ⏱️
To predict results before solving a problem 🔮
To check if an answer is reasonable ✅
Step 1: Round the Decimals 🎯
Round each decimal to the nearest whole number or nearest tenth.
Example:
3.76 → 4️⃣ (nearest whole)
5.42 → 5️⃣ (nearest whole)
Step 2: Add or Subtract the Rounded Numbers ➕➖
Addition Example: 3.76 + 5.42 ≈ 4 + 5 = 9
Subtraction Example: 8.35 − 2.47 ≈ 8 − 2 = 6
Step 3: Check Your Estimate ✅
Make sure the estimate is close to the actual answer.
It may not be exact, but it gives a reasonable idea of the result.
Tips for Estimating Decimals: ✨
Round up if the digit is 5 or more ⬆️
Round down if the digit is less than 5 ⬇️
Use mental math to make estimation faster 🧠
Fun Trick: 🪄
When adding several decimals, round first, then add → quick estimate!
When subtracting, round each number first → easy to calculate.
Example in Action: 🎉
Find an estimate for 6.48 + 3.27
- Round: 6.48 → 6, 3.27 → 3
- Add: 6 + 3 = 9 ✅
Actual sum: 6.48 + 3.27 = 9.75 → estimate is close!
Remember: 📝
Estimation doesn’t give exact answers
But it helps understand numbers better and solve problems faster! ⚡
Learn with an example
Estimate the sum by rounding each number to the nearest whole number and then adding.
9.78 + 3.49
The sum is approximately_________
Round each number to the nearest whole number.
9.78 + 3.49 = ?
10 + 3 = ?
Now add:
10 + 3 = 13
The sum is about 13.
Estimate the sum by rounding each number to the nearest whole number and then adding.
5.01 + 1.98
The sum is approximately _________.
Round each number to the nearest whole number.
5.01 + 1.98 = ?
5 + 2 = ?
Now add:
5 + 2 = 7
The sum is about 7.
Estimate the sum by rounding each number to the nearest whole number and then subtracting.
9.78 − 3.49
The difference is approximately_________
Round each number to the nearest whole number.
9.78 − 3.49 = ?
10 − 3 = ?
Now subtract:
10 − 3 = 7
The difference is about 6.
Estimate the sum by rounding each number to the nearest whole number and then subtracting.
9.21 − 3.69
The difference is approximately_________
Round each number to the nearest whole number.
9.21 − 3.69 = ?
9 − 4 = ?
Now subtract:
9 − 4 = 5
The difference is about 5.
Let’s practice!
