Mathematics for IGCSE & O level - Estimation (Section 3 - No. 26)
What is the general method to estimate answers to problems?
Round each number to one significant figure and perform the calculation.
Round each number to two significant figures and perform the calculation.
Calculate the exact answer and then round it.
Use a calculator for precise results.
Explication
To estimate, round each number in the problem to one significant figure and then perform the calculation.