Hi
Quick question for the S1 exam tomorrow. I had a quick search through previous posts, but was yet to find a definitive answer to my question.
How are we meant to work out quartiles? (Edexcel AS S1)
I had been taught to use:
Q1 = (n+1)/4
Q2 = (n+1)/2
Q3 = 3(n+1)/4
but the answers given by these seem to disagree with exam papers, like, for example, when n=50. My quartile terms are now:
Q1: 12.75th term
Q2: 25.5th term
Q3: 38.25th term
My questions are these:
1. Do I use the rule of thumb: "Use 'n+1' for n<100"
2. Do I round anything that's not a half?
ie using the example above,
Q1 = 12.75th term => Q1 = 13th term
Q3 = 38.25th term => Q3 = 38th term
I had been using interpolation, but this hadn't been giving the correct answers, so should I be rounding instead?
Thanks