Calculate the mean of the following distribution using step - deviation method.
Class IntervalFrequency30−401040−50650−60860−701270−80580−909
Class IntervalFrequency(fi)xiui=xi−ahfiui30−401035−3−3040−50645−2−1250−60855−1−860−701265=a0070−805751580−90985218 ∑fi=50 ∑fiui=−27
∴Mean=a+h∑fiui∑f
=65+10×(−27)50=65−5.4=59.6