t(c) An aero plane travelled a distance of 400 km at an average speed of x km/h. On the return journey, the speed was increased by

1 thought on “t(c) An aero plane travelled a distance of 400 km at an average speed of x km/h. On the return journey, the speed was increased by”

1. Step-by-step explanation:

   Given,

   Distance = 400 km

   Average speed of the aeroplane = x km/hr

   And, speed while returning = (x+40) km/hr

   We know that,

   Time = Distance / Speed

   (i) Time taken for onward journey = 400/x hrs

   (ii) Time taken for return journey = 400/(x+40) hrs

   Then, according to the question

   x

   400

   −

   x+40,

   400

   =

   60

   30

   x(x+40)

   400x+16000−400x

   =

   2

   1

   x(x+40)

   16000

   =

   2

   1

   x

   2

   +40x−32000=0

   x

   2

   +200x−160x−32000=0

   x(x+200)−160(x+200)=0

   (x+200)(x−160)=0

   So, x=−200 or 160

   As the speed cannot be negative, x = 160 is only valid.

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