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 34 feet and a minor axis of 16 feet, how far apart are the foci?

Answer 1

Better review the properties of an ellipse.
You have a=17 and b=8
Now, each focus is at a distance c from the center, where
b^2 + c^2 = a^2

(recall your basic Pythagorean triples here, to save time)