Question

A diver is 10 feet below the surface of the water and then descends 20 feet.what is the location of the diver after the descent??

Answer 1

First, the diver is 10 feet below the surface of the water, which is -10 feet. Then, it descends 20 feet again, which is -20 feet.
You will have to add -10 by -20 and then you will get -30 feet in total. 
So, the location of the diver after the descent would be -30 feet below the surface of the water.

I hope this helps :)

Answer 2

Answer:

-30 feet below