Pipe A is an inlet pipe that can fill an empty cistern in 8.7 hours. Pipe B can drain a filled cistern in 5.8 hours. When the cistern was filled the two pipes are opened one at a time for an hour each, starting with Pipe B. How long will it take for the cistern to be empty?

Which key on a windows keyboard sets to full screen mode in most browsers?

Let n be the number of different 5-digit numbers divisible by 4, with the digits 4, 5, 6, 7, 8 and 9, no digit being repeated in the numbers. What is the value of n?

The ratio of the area of a square to the area of a reenlar hexagon. having the same perimeter is:

Find the value of 335 * 335 - 165 * 165?