Question

A rock is thrown into a lake from a bridge 133 feet above the lake's surface. The rock sinks 78 feet below the lake's surface. What is the difference between the elevations?

Answer 1

211 feet

Explanation:

Consider vertical number line, where 0 is at surface of the lake, positive direction - above the lake surface and negative direction - below the surface of the lake.

A rock is thrown into a lake from a bridge 133 feet above the lake's surface, then initial position of the ball was +133.

The rock sinks 78 feet below the lake's surface, then the final rock's position is -78.

Difference: +133 - (-78) = 133 + 78 = 211 feet