If a pebble is dropped into a pond in the shape of an ellipse at the location of one focus, the waves will converge at the location of the other focus. if the pond has a major axis of 40 feet and a minor axis of 24 feet, how far apart are the foci?

The two foci are 64 feet apart. For an ellipse centered at (0,0), the formula for the distance from one focus to the origin is \sqrt(a^2-b^2), where a is the length of the major axis and b is the length of minor axis. In this case, \sqrt(40^2-24^2)=32. Since the two foci are symmetric about the origin, their distance in between is 2*32=64.