How much time is required to cover the distance of 910 Km by a car driver, if he start with the initial speed of 40 Km/hr. and increases the speed by 5 Km/hr for every next hour ?

• IT is AP series problem where
  a= 40, d=5 , sum = 910
  and n=?
  
  910 = (n/2)*(2*40+(n-1)*5)
  5n^2+75n-1820=0
  n^2+15n-364=0
  solving it, we get
  n=13
  
  so 13 hours
• 11 years agoHelpfull: Yes(5) No(1)
• 13hrs need to cover the distance of 910km.
  
  1st hour he crosses = 40km
  2nd hour he crosses = 85km (since 5km/hr increases every hour)
  3rd hour he crosses = 135km (since 5km/hr increases every hour)
  ..
  ..
  ..
  ..
  ..
  12th hour he crosses = 810km (since 5km/hr increases every hour)
  13th hour he crosses = 910km (since 5km/hr increases every hour)
  
  i.e, 40+45+50+55+60+65+70+75+80+85+90+95+100 = 910km
• 11 years agoHelpfull: Yes(2) No(2)
• 13 hours required to cover the distance of 910km.
  
• 11 years agoHelpfull: Yes(0) No(2)
• It can be solved by Arithmetic Progression.
  a= 40, d=5 , sum = 910.
  using the formul
  S=n/2*(2d+(n-1)*5);
  910 = (n/2)*(2*40+(n-1)*5)
  5n^2+75n-1820=0
  n^2+15n-364=0
  solving it, we get
  n=13 hrs (Ans)
  
  
  
• 11 years agoHelpfull: Yes(0) No(3)