Adding and Subtracting with Rational Numbers The elevation we call sea level is actually the
average level of the sea. This means that at
average sea level, the elevation is zero. In
reality, the level of the sea rises and falls in
what are called tides. Low tide is the point of
lowest sea level in a tidal period. High tide is
the point of highest sea level in a tidal period.
The height above or below average sea level is
called elevation. An elevation below sea level
is considered a negative value, while an
elevation above sea level is positive.
Winston lives near the ocean. He regularly
brings an altimeter to the beach to measure the
elevation of the ocean's surface. You will use
the data Winston gathered to complete tasks
about the rising and falling of the ocean's
surface. When necessary, sketch a diagram of
the situation on a separate sheet of paper to
assist you.
On Monday at 1 p. m., when the ocean's surface
was at an elevation of 2.2 feet, Winston went to
a surf shop that was 8.2 feet above the ocean's
surface. At 7 p. m. when the ocean's surface
was at an elevation of -2.4 feet, Winston ate
dinner at a restaurant whose deck was 10 feet
above the ocean's surface.

What was the net change in the elevation of
the ocean's surface from 1 p. m. to 7 p. m.?

Part B
How many feet apart are the two ocean
elevations described in part A?

Part C
What is the elevation of the deck where
Winston ate dinner?

Part D
What is the elevation of the surf shop?

Part E
What was the distance between the deck and
the ocean's surface at 1 p. m.? Which was
higher, the deck or the ocean?

Part F
What was the distance between the surf shop
and the ocean's surface at 7 p. m.? Which was
higher, the surf shop or the ocean?