in a race u drove 1st lap with 40kmph and in the second lap at what speed u must drive so that ur average speed must be 80kmph.

• cannot be determined
  that is average speed= (2*speed1*speed2)/(speed1+speed2)
  but here.......................................................................
  80=2*40*x/(40+x)
  cannot be solved
  or in otherwise x is infinity
• 14 years agoHelpfull: Yes(24) No(8)
• 80=2*40*u/40+u then next step 80=80/[(40/u)+1] this is possible only when u=infinity
  
• 12 years agoHelpfull: Yes(9) No(3)
• Infinite speed.
  Let distance of lap be d km. Total distance = 2d km. Time for first lap = d/40 kmph and that for second lap = d/x kmph, where x is rqd speed. Average speed = (total distance)/ (total time) = 2d/(d/40+d/x) = 2/(1/40+1/x). Given this is equal to 80. So, 2/(1/40+1/x) = 80. i.e., 2 = 80*(1/40+1/x). Or, 2 = 2 + 80/x. Which means 80/x = 0. For that x must be equal to infinity.
• 14 years agoHelpfull: Yes(6) No(8)
• let 2nd lap speed be x
  so (40+x)/2 =80
  so 40+x = 80*2
  40+x = 160
  x=120
• 9 years agoHelpfull: Yes(1) No(11)
• (40+x)/2=80
  x=160-40
  x=120
  
  so ans=120kmph
• 9 years agoHelpfull: Yes(0) No(7)
• avg speed= 2*x*y/x+y
  is only applied when certain part of whole journey is travelled with speed of x and other with y
  but this is not the case here
  one lap is a completete lap and second one is too.
  so, avg speed =40+x/2=80 i.e, x=120
• 5 years agoHelpfull: Yes(0) No(0)