A spherical iron ball of radius 10 cm is coated with a layer of ice of uniform thickness that melts at a rate of 50 cm³ /min. When the thickness of the ice is 5 cm, then the rate at which the thickness (in cm/min) of the ice decreases, is :

The number of real roots of the equation
5 + |2^x – 1| = 2^x (2^x – 2) is

If $$\mathop {\lim }\limits_{x \to 1} {{{x^2} - ax + b} \over {x - 1}} = 5$$, then a + b is equal to :

Minimum number of times a fair coin must be tossed so that the probability of getting at least one head is more than 99% is :