This is a question from my son's test. He got (a) correct but (b)wrong. He doesn't understand why. Would appreciate an explanation that can help him understand his mistake.
A submarine is at −750 feet or 750 feet below sea level. It descended 300 feet, then ascended 550 feet, and then descended 425 feet.
a. Write and evaluate a numerical expression to find the submarine’s final elevation. His answer is -925 feet which is correct.
b. The submarine next descended to the ocean floor, which was at an elevation of −2,250 feet. How far did the submarine descend?
He answered -1325 feet because according to his understanding the submarine descended so should be negative. However, the correct answer should be 1325 ft (not - 1325 ft). Please help him understand why.
Greatly appreciate your help, as always.