Find the mean of the step deviations:
Class intervalFrequency(fi)Class mark(xi)di=xi−aui=dih0−1004050−200−2100−20039150−100−1200−3003425000300−400303501001400−500454502002
1188
Class intervalFrequency(fi)Class mark(xi)di=xi−aui=dihfiui0−1004050−200−2−80100−20039150−100−1−39200−30034250000300−40030350100130400−50045450200290Total∑fi=188∑fiui=1
Mean of step deviations =∑fiui∑fi=1188