Solution:

Arranging the observations in ascending order

21, 23, 25, 26, 27, 28, 29, 29, 30, 31, 31, 35, 35, 38, 41, 42, 45, 47, 53

Here n = 19 which is odd.

(i)Median = ((n+1)/2)^th term

= (19+1)/2

= 20/2

= 10^th term

= 31

Hence the median is 31.

(ii) Lower quartile, Q₁ = ((n+1)/4) ^th term

= (19+1)/4

= 20/4

= 5 ^th term

= 27

Hence the lower quartile is 27.

(iii)Upper quartile, Q₃ = (3(n+1)/4) ^th term

= (3×(19+1)/4) ^th term

= (3×(20/4)) ^th term

= (3×5) ^th term

= 15 ^th term

= 41

Hence the upper quartile is 41.

(iv)Interquartile range = Q₃-Q₁

= 41-27

= 14

Hence the Interquartile range is 14.