Mode of value inside a modal class =  l + (f1f02f1f0f2)×h
     
	       where   l =  lower limit of the modal class,
				h =  size of the class interval (assuming all class sizes to be equal),
				f1  =  frequency of the modal class,
				f0  =  frequency of the class preceding the modal class,
				f2  =  frequency of the class succeeding the modal class.