Class interval:



0-6



6-12



12-18



18-24



24-30



Frequency:



7



5



10



12



6


Let the assumed mean (A) = 15


Class interval



Mid value (xi)



di = xi - 15



ui =



Frequency (fi)



fiui



3 – 6



3



-12



-2



7



-14



6 – 12



9



-6



-1



5



-5



12 – 18



15



0



0



10



0



18 – 24



21



6



1



12



12



24 - 30



27



12



2



6



12







N = 40



∑fiui = 5



We have, A = 15


h = 6


Mean = A + h *


= 15 + 6 *


= 15 + 0.75 = 15.75


8