Class mark	Frequency
12.5	12
17.5	17
22.5	22
27.5	27
32.5	30
37.5	21
42.5	16

(a) From the distribution, given above, construct a frequency table.

(b) Use the table obtained in part (a) to draw : (i) a histogram, (ii) an ogive.

(a) Since, the difference between the values of any two consecutive class marks is 5 (17.5 - 12.5).

Therefore, subtract $\dfrac{5}{2}$ = 2.5, from each class mark to get the lower limit of the corresponding class interval and add 2.5 to each class mark to get the upper limit.

Thus, the given cumulative frequency distribution table will be of the form :

(b) (i) Steps of construction of histogram :

1. Since, the scale on x-axis starts at 10, a break (kink) is shown near the origin on x-axis to indicate that the graph is drawn to scale beginning at 10.

2. Take 2 cm along x-axis = 5 units.

3. Take 1 cm along y-axis = 5 units.

4. Construct rectangles corresponding to the above continuous frequency distribution table.

The required histogram is shown in the below figure:

(ii) Steps of construction of ogive :

1. Since, the scale on x-axis starts at 10, a break (kink) is shown near the origin on x-axis to indicate that the graph is drawn to scale beginning at 10.

2. Take 2 cm = 5 units along x-axis.

3. Take 1 cm = 20 units along y-axis.

4. Ogive always starts from a point on x-axis representing the lower limit of first class. Mark point (10, 0).

5. Take upper class limits along x-axis corresponding cumulative frequencies along y-axis, mark the points (15, 12), (20, 29), (25, 51), (30, 78), (35, 108), (40, 129) and (45, 145).

6. Join the points marked by a free hand curve.

The required ogive is shown in the below figure: