Another S1 question

Was doing november 04 paper, and made slight error on the first part.

When finding Q1 Q2 and Q3 from a box plot, say the value you need is the 31.5th value. The answer implied that you were meant to round up so you read off the 32nd value. Is that only if the data is discrete, and say for example sake, the 43.25th value was needed, would you round down and read off the 43rd value, or round up to the next value of 44th.

while on this kind of topic, when is the mean (n+1)/2 or n/2. the book didn't really make much sense. is it just to do with whether the data is continuous or discrete.

thanks a lot.

Reply 1

*LEGEND*

What i do is:
If the total frequency is an even number like 60, then the median should be 30, not 60+1/2 = 30.5

But if the total frequency is given as 61, then its better to add one then divide. All the exam papers seem to follow this rule.
Is that okay?

Reply 2

driving_seat

My teacher told a very good technique

in all of the terms just add 1 and remeber the following tips. It works with both and even terms.

to find median use: (n+1)/2 it is a whloe numer for odd and .5 for even for example if u have 11 terms then median is 6th term but if u ve 30 terms it will come to be 15.5th term, so u ve to take 15th and 16th term and take average of the terms

The same procedure can be applied to find Upper Quartile and Lower Q
use (n+1)*3/4 and (n+1)*¼ respectively
Conclusion
If the term is in decimal then take the adjecent terms of that number which are whole number and take average.

e.g. u get when calculating upper quartile 17.25th term, take 18th term and 17th term and take average.

I hope that helps