🎯 Estimation & Number Sense
Learn to estimate answers and understand place value
🎯 What is estimation?
Estimation means figuring out roughly what an answer should be, without calculating exactly. It's one of the most useful skills in maths — and in life.
Think: "About how big is the answer?"
Instead of computing 88 × 888 exactly, you can think: 88 is close to 100, and 888 is close to 900. So 100 × 900 = 90,000. The answer is somewhere around there.
🔢 Rounding to make life easier
The key trick: round numbers to something simple, then multiply or add.
Example: Is 88 × 888 closer to 8,000 or 80,000?
- 88 is between 80 and 100
- 888 is between 800 and 1000
- 80 × 800 = 64,000 and 100 × 1000 = 100,000
- So the answer is between 64,000 and 100,000 → it's in the range of tens of thousands
🧪 Try it: The estimation machine
Pick two numbers and estimate their product by rounding.
88
888
Rounded: 100 × 900
≈ 90,000
Exact answer: 78,144
Notice: the estimate doesn't need to be exact — it just needs to tell you the right ballpark. Is it in the hundreds? Thousands? Tens of thousands?
📐 Place value: what each digit is worth
Understanding place value helps you estimate. In the number 4,897:
- The 4 is worth 4,000 (thousands)
- The 8 is worth 800 (hundreds)
- The 9 is worth 90 (tens)
- The 7 is worth 7 (ones)
When three consecutive 4-digit numbers have missing digits, you can use place value to figure them out. If one number ends in 7 and the next starts with a different thousands digit, there must have been a "rollover" (like 3999 → 4000).
⚡ Quick tricks
- Multiplying by near-100: 88 × 888 → think 88 × 900 = 79,200 (close enough!)
- Adding big sums: 2023 − 3 − 25 + 2024 − 3 − 23 → group: (2023+2024) − (3+25+3+23) = 4047 − 54 = 3993
- Consecutive numbers: Three in a row like ___7, _898, 48__ → the middle one is 4898, so they're 4897, 4898, 4899
🧠 Practice Quiz
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