Two towns A and B are 60 km apart. A school is to be built to serve 150 students in town A and 50 students in town B. If the total distance to be travelled by all 200 students is to be as small as possible, then the school should be built at

If p, q, r are any real numbers, then

The largest interval for which $${x^{12}} - {x^9} + {x^4} - x + 1 > 0$$ is

Both the roots of the equation (x - b) (x - c) + (x - a) (x - c) + (x - a) (x - b) = 0 are always