Two tangents are drawn to a circle which touch the circle at points A and B. The maximum distance between the points A and B is :

1. radius of the circle

2. diameter of the circle

3. π × radius of the circle

4. π × diameter of the circle

In the given figure, ac = y units, BC = x units, then the height of DC is :

1. $\sqrt{x + y}$

2. $\sqrt{xy}$

3. $\sqrt{y - x}$

4. $\sqrt{\dfrac{y}{x}}$

The mean of n observations is M. If one of these observations is misread as 60 instead of 50, the correct mean is:

1. M - 50 + 60

2. M × n - 60 + 50

3. $\dfrac{M \times n - 60 + 50}{n}$

4. $\dfrac{M \times n - 50 + 60}{n}$

The given figure shows a right triangle ABD with sides 15 cm, 20 cm and 25 cm. The triangle is revolved about its hypotenuse, find the volume of the double cone so formed. (Take $\pi = 3\dfrac{1}{7}$)