21.

The table below shown the salaries of 280 persons:

Salary (In thousand)	No. of Person
5-10	49
10-15	133
15-20	63
20-25	15
25-30	6
30-35	7
35-40	4
40-45	2
45-50	1

Calculate the median salary of the data.

A wooden article was made by scooping out a hemisphere from each end of a solid cylinder, as shown in Fig. If the height of the cylinder is 10 cm and its base is of radius 3.5 cm. Find the total surface area of the article.

A heap of rice is in the form of a cone of base diameter 24m and height 3.5 m. Find the volume of the rice. How much is canvas cloth required to just cover the heap?

Find the area of the shaded region in Figure, where arcs are drawn with centres A, B, C and D intersect in pairs at mid-points P, Q, R and S of the sides AB, BC, CD and DA respectively of a square of side 12 cm, [Use π =3.14 ]

If $4 \tan \mathrm{\theta } = 3, \mathrm{evaluate} \left(\frac{4 \sin \mathrm{\theta } - \cos \mathrm{\theta } + 1}{4 \sin \mathrm{\theta } + \cos \mathrm{\theta } - 1}\right)$

If tan 2A = cot (A - 18^o), where 2A is an angle, find the value of A

As observed from the top of a 100 m high light house from the sea-level, the angles of depression of two ships are 30° and 45°. If one ship is exactly behind the other on the same side of the light house, find the distance between the two ships. [ Use √3= 1.732 ]

The diameters of the lower and upper ends of a bucket in the form of a frustum f a cone are 10 cm and 30 cm respectively. If its height is 24 cm, find:

(i) The area of the metal sheet used to make the bucket.
(ii) Why should we avoid the bucket made by ordinary plastic? [ Use π =3.14 ]

Prove that $\frac{\sin \mathrm{A} - 2{\sin }^3 \mathrm{A}}{2 {\cos }^3 \mathrm{A} - \cos \mathrm{A}} = \tan \mathrm{A}$.

The mean of the following distribution is 18. Find the frequency f of the class 19-21.

Class	11-13	13-15	15-17	17-19	19-21	21-23	23-25
Frequency	3	6	9	13	f	5	4