What is the first quartile (q1) of the data set? 51, 42, 46, 53, 66, 70, 90, 70
80
59.5
61
48.5

Values in increasing order 
42 
46 
51 
53 
66 
70 
70 
90 

Lower quartile : There are 8 observations 
If there are in observations, compute the lower quartile as follows: 
if n/4 is an integer, compute the lower quartile as 
(x[n/4]+x[n/4+1])/2 :: (x[8/ 4]+x[8 /4 +1])/2 
if n/4 is not an integer, compute the lower quartile as 
x[k], where k is the smallest integer exceeding n/4:: 2 = 2 
Lower Quartile : Average of observations 2 and 3 is -- 
= (46+51)/2 = 48

Lines that intersect at one point