John traveled 80% of the way from Yellow-town to Green-fields by train at an average speed of 80 miles per hour.The rest of theway John travelled by car at an average speed of v miles per hour.If the average speed for the entire trip was 60 miles per hour ,What is v in miles per hour?

• avg.speed = (d1+d2)/(t1+t2)
  
  let us assume total distance=100 miles
  d1 = 80% of 100 which is 80 miles.
  d2 = (100-80) which is equal to 20 miles.
  t1 = time taken by train which is 80/80 = 1hr.
  t2 = time taken by car 20/v hrs
  
  60 = (80 + 20) / ( (80/80) + (20/v) )
  
  v = 30 miles per hour.
• 11 years agoHelpfull: Yes(67) No(0)
• 2*80*v/80+v=60
  --> v=48mph
  
  
  
• 11 years agoHelpfull: Yes(6) No(18)
• 30 mph
  avg spd=total distance/total time
  60=(80+20)/(80/80)+(20/v)
  =>v=30
• 11 years agoHelpfull: Yes(6) No(0)
• 6 hours
  assume 1 ltr in beginning ..in 8 hors capacity=2^7=128lts (total capacity)
  1/4th capacity= 32 ltrs =2^5 => 5+1=6hrs
  
  
• 11 years agoHelpfull: Yes(2) No(5)
• x/((0.80*x/80 + 0.20/v))= 60,
  So, v= 30 miles/hr Ans.
• 11 years agoHelpfull: Yes(2) No(1)
• ans=75mph
  assume total 100 miles => total speed= total distance/total time= (100)/(4/3)=75
• 11 years agoHelpfull: Yes(1) No(10)
• ans=40
  let dis be100 and speed be x
  then
  80*80+x*20=60*(80+x)
  6400+20x=4800+60x
  solving we get x=40ans
• 11 years agoHelpfull: Yes(1) No(12)
• 60=(80+20)/((80/80)+(20/v))
  v=30
• 5 years agoHelpfull: Yes(0) No(0)