A plane flies a distance of 1600 km at a certain speed. On the return journey, due to bad weather, as the speed was reduced by 40 km/hr it took 1 hour 20 minutes more than the onward journey. Find the speed of the onward journey.

Asked by khushdab | 2nd Apr, 2020, 04:37: PM

Expert Answer:

Let the speed of the journey be x km/hr and t be the time taken at an average speed x km/hr.
I f space t h e space s p e e d space i s space r e d u c e d space b y space 40 space k m divided by h r comma space t h e space t i m e space t a k e n space i s space 1 space h r space 20 space m i n u t e s space m o r e space t h a n space t h e space o n w a r d space j o u r n e y
rightwards double arrow fraction numerator 1600 over denominator x minus 40 end fraction minus 1600 over x equals 1 plus 20 over 60 equals 4 over 3
rightwards double arrow 1600 open parentheses fraction numerator x minus x plus 40 over denominator x squared minus 40 x end fraction close parentheses equals 4 over 3
rightwards double arrow fraction numerator 16000 over denominator x squared minus 40 x end fraction equals 1 third
rightwards double arrow x squared minus 40 x minus 48000 equals 0
rightwards double arrow x equals fraction numerator 40 plus-or-minus square root of 1600 plus 192000 end root over denominator 2 end fraction equals fraction numerator 40 plus-or-minus 440 over denominator 2 end fraction
rightwards double arrow x equals 240 space o r space minus 200
S i n c e comma space t h e space s p e e d space c a n apostrophe t space b e space n e g a t i v e.
H e n c e comma space t h e space s p e e d space o f space t h e space o n w a r d space j o u r n e y space i s space 240 space k m divided by h r

Answered by Renu Varma | 3rd Apr, 2020, 11:30: AM