The value of a single discount on some amount which is equivalent to a series of discounts of 10%,20% and 40% on the same amount is equal to

Which one of the following is correct? 

A and B are two taps which fill a tank individually in 10 minutes and 20 minutes respectively.However,there is a leakage at the bottom,which can empty a filled tank in 40 minutes.If the tank is empty initially,how much time will both taps take to fill the tank with leakage?

If a,b and c satisfy the equation x³-3x²+2x+1=0,then what is the value of 1/a+1/b+1/c

The seven digit number 876p37q is divisible by 225.The values of p and q can be respectively

If (x+1) is the H.C.F of Ax²+Bx+C and Bx²+Ax+C where A≠B,then the value of C is