A miner descended 1500 feet into a mine. While in the mine, he then rose 1200 feet and then descended 850 feet. What was the miner's net gain or loss in altitude?

Call descending a negative number and rising a positive number.

Then add the numbers.

A miner descended 1500 feet into a mine.

-1500 ft

he then rose 1200 feet

+1200 ft

then descended 850 feet

-850 ft

Now add the three numbers:

-1500 ft + 1200 ft + ( - 850 ft) = - 1150 ft

Since the sum is a negative number, that means

he had a net loss in altitude of 1150 ft.