Alternative methods for computing percentile

Sir, in part 3 of this topic u used 0.5 for computing the percentile, if the value is not integer but what if the value is 18.9 then we can’t take 0.5 as 18.2 is more close to 18 but 18.9 is more close to 19 then this approximation will not be good

Yes, which is one of the reasons that it’s suggested to use the first alternative. But there can be different systems which also use the 3rd one considering some other perspectives.