The following histogram shows the frequency distribution f the ages of 22 teachers in a school:

(i) The eldest $(50-55$ years) $=1$ person

This is because the height of the rectangle with class interval $50-55$ as base is 1 unit.

The youngest $(20-25$ years $)=2$ persons

This is because the height of the rectangle with class interval $20-25$ as base is 2 units.

(ii) The group containing the most number of teachers is $35-40$ years. This is because the height of the rectangle with class interval $35-40$ as base is the maximum.

The group containing the least number of teachers is $50-55$ years. This is because the height of the rectangle with class interval $50-55$ as base is the minimum.

(iii) Class size = The range between the upper and the lower boundaries of the class

For example, the size of the class $20-25$ years is 5 .

(iv) Class mark $=\frac{\text { Upper limit }+\text { Lower limit }}{2}$

For class $20-25$ :

Class mark $=\frac{20+25}{2}=\frac{45}{2}=22.5$

Similarly, the class marks of the other classes are 27.5; 32.5; 37.5; 42.5; 47.5; 52.5.