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.
Explication
Round each number to one significant figure before multiplying.