If you are aware of elementary facts of geometry, then you might know that the area of a circle with radius $ R$ is $ \pi R^2$ . The radius

# Calculation

Before my college days I used to multiply this way. But as time passed, I learned new things. In a Hindi magazine named “Bhaskar Lakshya”, I read an article in which

Let have a Test: You need to make a calculation. Please do neither use a calculator nor a paper. Calculate everything “in your brain”. Take 1000 and add 40. Now,