Multi-Digit Multiplication • Topic 3 of 3

Estimate Products Before Calculating

Estimation helps us check if our answer is reasonable. We round numbers to a convenient value before multiplying.

How to Estimate:

  • Round each number to the nearest 10, 100, or 1,000
  • Multiply the rounded numbers
  • Compare with the actual answer — they should be close

Estimation is especially useful to detect calculation errors!

Estimation: 487 x 32Estimate487 rounds to 50032 rounds to 30500 x 30 = 15,000Actual487 x 32= 15,584Estimate (15,000) is close to actual (15,584) — answer is reasonable!
Solved Examples
1
Worked Example
Estimate and then find the actual product of 487 x 32.
SolutionEstimate: 487 rounds to 500; 32 rounds to 30. Estimate = 500 x 30 = 15,000. Actual: 487 x 32 = 15,584. The estimate (15,000) is close to the actual (15,584).
2
Worked Example
Estimate 2,345 x 7.
SolutionRound 2,345 to 2,000. Estimate = 2,000 x 7 = 14,000. Or round to 2,300: 2,300 x 7 = 16,100. Actual: 2,345 x 7 = 16,415. Both estimates are in the right range.
3
Worked Example
A farmer harvests 1,236 kg of wheat per day. Estimate how much he harvests in a week (7 days).
SolutionRound 1,236 to 1,200. Estimate = 1,200 x 7 = 8,400 kg. Actual: 1,236 x 7 = 8,652 kg. The estimate (8,400) is a good approximation.

Key Points

  • Round numbers to the nearest 10, 100 or 1,000 before estimating
  • Estimation catches big errors in your calculations
  • The actual answer should be close to the estimated answer
  • Useful in real life when exact calculations are not needed
Quick Check — 4 MCQs
Tap an option to check your answer0 / 4
Q1.To estimate a product, you first:
Explanation: Round, then multiply.
Q2.$48\times21$ is about:
Explanation: $50\times20=1000$.
Q3.Rounding $31$ to the nearest ten gives:
Explanation: $30$.
Q4.An estimate is:
Explanation: Close, not exact.
Practice more MCQs → 📝 Assignment · 35 marks