Question

Brenda observes that the keyboard and the screen of an open laptop lie on two different planes. In how many lines do the planes containing the keyboard and the screen intersect?

Answer 1

Let's assume the laptop is opened at 90 degrees (this is done for the sake of simplicity, is actually irrelevant) then each plane would be analogous to the 'x' and 'y' planes you see in a Cartesian Plane, which only intersect at one point called the Origin. Any two lines with different slopes will intersect only one time (if they're parallel they have the same slope)