The speed of a bus during the second hour of its journey is twice that in the first hour. Also, its speed during the third hour is two-third the sum of its speeds in the first two hours. Had the bus travelled for three hours at the speed of the first hour, it would have travelled 120 km less. Find the average speed of the bus for the first three hours.

A.

60 kmph

B.

70 kmph

C.

80 kmph

D.

100 kmph

• let 1st hr speed be xkm/hr,then
  2nd hr speed is 2x km /hr and 3rd hr speed=2/3(x+2x)=2x
  now,3x-x=120
  x=60
  therefore average spped for first 3 hrs=(60+120+120)/3
  =100 km /hr(ans)
• 11 years agoHelpfull: Yes(1) No(0)
• Let,the speed for first hour = s km/hr
  for second hour it become twice i.e.= 2s km/hr
  for third hour = 2/3 (2s+s)=2s km/hr
  total speed = s+2s+2s=5s km/hr
  the bus had travel 3hour at speed of 1st hour and travel 120km less =5s-3s=120
  i.e.s=60;
  average speed= 5s/3= (5*60)/3=100km
• 5 years agoHelpfull: Yes(0) No(0)