Alex is practicing his dives at a pool. He dives from a dividing board that is 21 feet above the surface of the water. His dive takes him 17 feet below the surface of the water. Alex says that the two distances are opposite, so his total dive distance is 22 + (-17) = 5 feet. Is Alex correct? How far did he travel if he is wrong?

NO. Alex was wrong.  

The total dive distance is 21 + 17 = 38 feet

Step-by-step explanation:

Alex was wrong because his direction of diving is from above the water through the surface of the water to under the water.

So his direction of travelling is not opposite but the same.

Therefore the total distance traveled by Alex = distance traveled from the diving board to the water surface + distance traveled from the water surface to down below the water  

Distance traveled from the diving board to the water surface = 21 feet

Distance traveled from the water surface down below the water = 17 feet  

Total distance traveled by Alex = 21 feet + 17 feet

   = 38 feet.

Thus, Alex was wrong because the the total distance traveled by Alex was 38 feet.