One way to get quartile points is get median(Q2), then the upper and lower sets and then find their median to get Q1 and Q3.
But, I have found this formula which says Q1 = (1/4)(n+1)th term where n is no. of terms in the set.
Similarly for Q2 = (2/4)(n+1)th term
and Q3 = (3/4)(n+1)th term
Let's say there is a set x = 5,10,15,20,25,30,35,40,45,50
So I know the Median is (25+30)/2 = 27.5 = Q2
and to find Q1 we can take median of lower set, i.e 5,10,15,20,25, which is 15 = Q1.
Similarly to find Q3 we can take median of upper set, i.e 30,35,40,45,50, which is 40 = Q3
But by using the formula, we get Q1 = 1/4(11) = 2.75th term. = 13.75
and Q2 = 2/4(11) = 5.5th term. i.e = 27.5
and Q3 = 3/4(11) = 8.25th term. i.e = 41.5
which gives me different inter quartile range. so which method should I use in the exam?
here is an example of the formula if you haven't heard of it before.
http://facstaff.cbu.edu/wschrein/media/M201%20Notes/M201L23.pdf