Mathematics for IGCSE & O level - Estimation (Section 4 - No. 2)

Which of the following is the best strategy for estimating the answer to a multiplication problem?

Calculate the exact answer and then round to 1 s.f.

Round all numbers to 1 significant figure and then multiply.

Use a calculator and record all the digits displayed.

Round the numbers to the nearest whole number, and then multiply.

Round each number to one significant figure before multiplying.