Use signed numbers to solve. a helicopter descended 1200 feet, rose 800 feet, and then descended 450 feet. what was the net gain or loss in altitude? a. lost 2450 ft b. lost 850 ft c. gained 850 ft d. gained 2450 ft

The rise or an increase in altitude is represented by positive sign and a decend or decrease in altitude is represented by negative sign. 

First the helicopter descended 1200 feet. So the change in altitude will be -1200 feet.

Then the helicopter rose by 800 feet. So the change in altitude will be 800 feet.

Finally the helicopter descended by 450 feet. So the change in altitude will be -450 feet.

The net change in altitude will be the sum of all the above 3 changes. 
Change in altitude = -1200 + 800 - 450 = -850 feet

The negative sign indicates a descend i.e. loss in altitude. So the net change in altitude was a loss of 850 feet.