Class interval:



0-8



8-16



16-24



24-32



32-40



Frequency:



6



7



10



8



9


Let the assumed mean (A) = 20


Class interval



Mid – value (xi)



di = xi - 20



ui =



Frequency (fi)



fiui



0 – 8



4



-16



-2



6



-12



8 – 16



12



-8



-1



7



-17



16 – 24



20



0



0



10



0



24 – 32



28



8



1



8



8



32 - 40



36



16



2



9



18







N = 40



fiui = 7



We have, A = 20


h = 8


Mean = A + h *


= 20 + 8 *


= 20 + 1.4 = 21.4


7