Concept 7 of 8Foundation
Watch on YouTubeVideoLarge-number operations & estimation
When numbers get big, exact arithmetic is slow. Use estimation to save time:
- Round each number to a convenient value (nearest 10, 100, 1000).
- Do the easy operation.
- Check: is the real answer near your estimate?
Front-end estimation: keep the leftmost digit, set the rest to zero.
Example: 4,876 → 4,000; 2,189 → 2,000 → sum ≈ 6,000.
Compatible numbers: replace with nearby numbers that are easier to compute. 498 × 21 ≈ 500 × 20 = 10,000.
Estimation is a superpower in olympiad MCQs — it often rules out 2–3 wrong options in seconds.
Example
A farmer sold 487 bags of wheat at ₹312 each. Estimate revenue:
≈ 500 × 300 = ₹1,50,000.
Exact = 487 × 312 = 1,51,944. Close!
≈ 500 × 300 = ₹1,50,000.
Exact = 487 × 312 = 1,51,944. Close!
💡 Tip:If your exact answer is wildly different from the estimate, you probably made a mistake.
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5 questions to check what you just read.
0 / 5
- Q1.Estimate 4,876 + 2,189 (nearest 1000):
- Q2.Quick estimate of 38 × 42:
- Q3.Estimate 3,987 ÷ 19 (front-end):
- Q4.Which is closest to 597 × 301?
- Q5.Sum 197 + 298 estimated to nearest 100: