A tank is fitted with two taps. The first tap can fill the tank completely in 45 minutes and the second tap can empty the full tank in one hour. If both the taps are opened alternately for one minute, then in how many hours the empty tank will be filled completely?

Two trains 108 m and 112 m in length are running towards each other on the parallel lines at a speed of 45 km/hr and 54 km/hr respectively. To cross each other after they meet, it will take

A and B together can plough a field in 10 hours but by himself A requires 15 hours. How long would B take to plough the same field?

A and B can separately complete a piece of work in 20 days and 30 days respectively. They worked together for some time then B left the work. If A completed the rest of the work in 10 days, then B worked for how many days?

The total surface area of a solid right circular cylinder is twice that of a solid sphere. If they have the same radii, the ratio of the volume of the cylinder to that of the sphere is given by

Which is the smallest prime number? 

Directions : What should come in place of the question mark (?) in the following number series? 

7 17 54 ? 1098 6591