A plane flies 420 miles with the wind and 350 miles against the wind in the same length of time. If the speed of the wind is 23 mph, what is the speed of the plain in still air?  Choose the correct option
A) 253 mph .
B) 275 mph .
C) 296 mph .
D) 278 mph .
E) 235 mph .

Rationale: the speed of the plane in still air = x miles / hour the speed of the wind is 23 mph speed with the wind = ( x + 23 ) mph speed against the wind = ( x – 23 ) mph time = distance / speed according to the problem , 420 / ( x + 23 ) = 350 / ( x – 23 ) 420 ( x – 23 ) = 350 ( x + 23 ) 420 x – 9660 = 350 x + 805 420 x – 350 x = 8050 + 9660 70 x = 17710 x = 17710 / 70 x = 253 therefore , the speed of the plane in still air = 253 mph . correct answer a
Answer: A