What is the elevation of the surface of the lake? Use absolute value to explain.

Question

The deepest point of Lake Titicaca in South America is -922 feet relative to its surface. The deepest point is 11,542 feet above sea level. What is the elevation of the surface of the lake? Use absolute value to explain.

Answer 1

The first sentence states that the deepest point...is -922 feet RELATIVE TO ITS SURFACE. This means that, regardless of what coordinate system is used or how it is oriented, the DISTANCE between these two locations (or points) is

|-922| = 922 feet.

So, restating, the deepest point...is a DISTANCE 922 feet below its surface. Note that the DISTANCE between two points is not dependent on any coordinate system, and that distance is always positive. If we travel upwards from sea level to the surface of the lake, or if we travel downward from the surface of the lake to sea level, the distance that we travel is the same.

The second sentence states that the deepest point is 11,542 feet above sea level. So the deepest point of the lake is 11,542 feet above sea level, and the surface of the same lake is 922 feet above that.

So we add those two numbers to get the elevation of the surface of the lake:

11,542 + 922 = 12,464 feet above sea level.