Which rounding off method to follow?

Question

In a book named " Concepts of Physics" by H.C Verma , it was said that " when there is 5 after the decimal point and the number immediately before the decimal point is an even number it doesn't change . Example - Rounding off 2.5 to nearest ones is 2"

But from my high school days I have been learning that 2.5 rounded off to nearest ones is 3 .

I am really confused what to follow ?

Answer 1

I was taught the same in High-School as well.

The rule went like this:-

A number in decimals, let's say "x.y" needs to rounded off,
then   
check whether y > 5, if yes, x.y = x+1  
check whether y < 5, if yes, x.y = x  
if y = 5, then check if x is even or odd,   
if even, x.y = x else x.y = x+1.

In life out of school, we follow the rules that best suit our purpose.

For example, rounding off numbers like above method might have made sense in a physics class involving measuring instruments, (like learning to use vernier calipers). These numbers are nothing but data.

In real life, data is used to represent a certain statistic that conveys some information. Rounding off a quantity, means to "compress" this data into more comprehensible units. Either you can say the elapsed time was 2.441s or 3 seconds. Or the shuttle missed its mark by 1.145cm or 1 centimeter.

In rounding off data, you decide between losing some data or gaining some garbage data; and which of them would be lesser of a problem.

One more example, sometimes we can "sample" some data for another system which could result in loss of some data (Analog to Digital Conversion).