Find the mean marks per student, using Assumed - mean method:


Marks



0 - 10



10 - 20



20 - 30



30 - 40



40 - 50



50 - 60



Number of students



12



18



27



20



17



6


We will find the mean marks per student using Assumed - mean method, where A = Assumed mean.


CLASS



MID - POINT(xi)



FREQUENCY(fi)



DEVIATION(di)


di = xi – 25



fidi



0 - 10



5



12



- 20



- 240



10 - 20



15



18



- 10



- 180



20 - 30



25 = A



27



0



0



30 - 40



35



20



10



200



40 - 50



45



17



20



340



50 - 60



55



6



30



180



TOTAL




100




300



We have got


A = 25, Σfi = 100 & Σfidi = 300


∵ mean is given by



⇒


⇒


Thus, mean is 28.


15