[6.05] Which set of equations would be used to solve this word problem?

An airplane flew 3.5 hours with a 40 mph head wind. The return trip with a tail wind of the same speed took 2.5 hours. Find the speed of the plane in still air.

d = 3.5(r + 40) and d = 2.5(r − 40)

d = 3.5(r − 40) and d = 2.5(r + 40)

d = 6(r + 40)

None of these systems can be used to solve this problem.

Question

[6.05] Which set of equations would be used to solve this word problem?

An airplane flew 3.5 hours with a 40 mph head wind. The return trip with a tail wind of the same speed took 2.5 hours. Find the speed of the plane in still air. 

 d = 3.5(r + 40) and d = 2.5(r − 40) 

 d = 3.5(r − 40) and d = 2.5(r + 40) 

 d = 6(r + 40) 

 None of these systems can be used to solve this problem.

anonymous · Answer

d = 3.5(r − 40) and d = 2.5(r + 40)  => r=(3.5+2.5)*40=6*40=240