How to find the lower an upper quartile given an even set of data?Take 2, 2.5 ,4,5.5,6,7 as an example!...

Quartiles are basically measures of central tendancy in a
group of data that divide it in four subgroups by three quartiles Q1, Q2 and
Q3.

Q1 - First Quartile - seperates first 1/4th data from
remaining 3/4th data (located at 25th
precentile)

Simillarly Q2 and Q3 are located 50th and 75th
percentile.

Now, the formula for finding quartile is i =
(P/100)*n where p = percentile and n = number of terms in
data.

If we get i=whole number, we take the quartile as the
average of ith term and (i+1)th from the data, eg. if i obtained is 3, we take average
of 3rd and 4th term as quartile

If "i" obtained is not
whole number, we simply take next term as quartile, eg. if i obtained is 3.75, we take
4th term as quartile.

In your
example,

Date = 2, 2.5, 4, 5.5, 6,
7

Q1(Lower Quartile), p=25, n=
6

i = (25/100)*6 = 1.5,

Since
i obtained is not a whole number, we take 2nd number as quartile, therefore Q1 =
2.5

Simillary for Q3(Upper Quartile), p=75,
n=6

i = (75/100)*6 = 4.5

Since
i obtained is not whole number, we take 5th number as quartile, therefore Q4 =
6.

Ans.:-

1) Lower Quartile Q1
= 1.5

2) Upper Quartile Q3 = 4.5