Given observations in ascending order: 4, 6, 8, 10, 10, 12, 14, 16, 18, 20. Q1 = N+1 4th observation Q1 = 10+1 4th observation Q1 = 11 4th observation Q1 = 2.75th observation Here, 2nd observation is 6 and now add 0.75* 2nd observation - 3rd observation to the 2nd observation . ⇒6 + 0.75*8-6 = 7.5 Therefore, 2.75th observation is 7.5. Q3 = 3N+1 4th observation Q1 = 310+1 4th observation Q1 = 11 4th observation Q1 = 8.25th observation Here, 8th observation is 18 and now add 0.25* 8th observation - 9th observation to the 8th observation . ⇒18 + 0.25*20-18 = 18.5 Therefore, 8.25th observation is 18.5. C.D. = Q3 - Q1 Q3 + Q1 = 18.5 - 7.5 18.5 + 7.5 = 0.4231