Manu started travelling from city A to city B.He stopped his journey for 60 minutes at a city C to watch his favourite live gameafter travelling one hour.Then he continued his journey at 4/5th of previous speed and reached his destination 1 hour 24 minutes late than he planned.if he stopped his journey to watch game for next 120 Km from city C,Manu could have reached 1 hr 12 minutes late than the time he planned.Find out the actual speed of Manu.
A)120kmph
B)150kmph
c)135kmph
D)155kmph

• b
  Let his initial speed be X kmph
  
  After reaching City B, let the distance yet to travel = D km
  
  Therefore D = Xt = 0.8X (t + 0.4) [where t is the planned time and 1 hr for match was already calculated]
  or, Xt = 0.8Xt + 0.32X
  or, 0.2Xt = 0.32X
  or, t = 1.6
  
  Therefore t= 1 hr 36min which was the planned time
  
  Now if he would have travelled 120km with speed Xkmph and then stopped for 1hr for the match and then continues with a speed of 0.8X kmph then time taken will be (t+0.2) i.e 1.6+0.2 = 1.8 hr
  
  Therefore t1(time taken to travel 120km with speed X) + t2(time taken to travel rest distance with speed 0.8X) = 1.8 hr
  
  or, 120/X + (1.6X-120)/0.8X = 1.8
  120/X + 2 - 150/X = 1.8
  30/X = 0.2
  X= 30/0.2 = 150
  
  Therefore actual speed = 150kmph
• 9 years agoHelpfull: Yes(0) No(0)