(GRE Success! ) time & Work Problems

1.Pipe A can fill a pool in 5 days and pipe B can fill the pool in 3 days .if they start working together at same time,how long(in hours) will it take to fill the pool. if pipe B stops working after a DAy??


2.if 2 trains, each 400m long, travel on parallel tracks at a speed of 90 mph in 30mph towards each other, then how long will it take to cross each other in seconds


Geometry

1.two squares of 6 cm intersect each other to form a regular octagon,find the perimeter of regular octagon


Please can any one Provide the solutions for this Problems