Qualification > Math

histogram and medians doubt!

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nid404:
Generally to find median in any grouped frequency one uses this formula - (n+1)/2 where n stands for the sum of frequencies. Take q3 for example where u need to find the median score. There are 320 students, so median is 160.5(using the formula). S0 u check which range the 160 and 161 student lies. This is between 90-110(by adding up the frequencies u get this(range * frequency density)) The hundredth student got a 90. So the 160th student got how much?
5(fre density)* x=60(frequency, 160-100)
x=12, therefore 160th student got 102.
and
5*x=61
x=12.2
161th student got 102.2
therefore median marks equal= (102+102.2)/2
=102.1

Correct me if i'm wrong. This is how i've been doin it. Mike Folland's textbook says this. Astar can explain in a better way i suppose but i thought i'll try.

astarmathsandphysics:
This looks ok to me but some books use n/2

nid404:
I was wondering if one can make a cumulative frequency graph using the data and then find out the median. It becomes easier.

SGVaibhav:
i think for finding median in a cumulative frequency graph, we have to have n/2.
for normal cases (n+1)/2.
am i right?

Christy:
ya .. ur right :D

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