From the following data compute the value of Harmonic Mean.

Marks	10	20	30	40	50
No. of students	20	30	50	15	5

An automobile driver travels from plain to hill station 100km distance at an average speed of 30km per hour. He then makes the return trip at average speed of 20km per hour what is his average speed over the entire distance (200km)?

Calculate the value of quartile deviation and its coefficient from the following data

Roll No.	1	2	3	4	5	6	7
Marks	20	28	40	12	30	15	50

Find Q₁, Q₃, D₈ and P₆₇ of the following data :

Siza of shares	4	4.5	5.	5.5	6	6.5	7	7.5	8
Fequency	10	18	22	25	40	15	10	8	7

The price of a commodity increased by 5% from 2004 to 2005, 8% from 2005 to 2006 and 77% from 2006 to 2007. Calculate the average increase from 2004 to 2007?