Question

Find the mean and median for the following data:

Classes:	5-15	15-25	25-35	35-45	45-55	55-65	65-75
Frequencу:	2	3	5	7	4	2	2

Answer 1

The class marks are 10, 20, 30, 40, 50, 60 and 70.

\[N=25,\quad \sum f_i x_i=970\] 

\[\text{Mean}=\frac{970}{25}=38.8\] 

For the median, `N/2 = 12.5`.

The cumulative frequency first exceeding 12.5 is 17, so the median class is 35-45.

Here l = 35, h = 10, f = 7 and F = 10.

\[\text{Median}=35+\frac{12.5-10}{7}\times 10\approx 38.57\] 

Hence, the mean is 38.8 and the median is approximately 38.57.