Mohan takes 8 days less than the time taken by Ravi to finish a piece of work. If both Mohan and Ravi together can finish it in 7.5 days, then how many days Ravi will take to finish the work alone ?

1) 15 days
2) 18 days
3) 20 days
4) 24 days
5) 28 days

• 3) 20 days
  
  Let the time taken by Ravi to finish the work be 'x' days, then Mohan takes 'x-8' days.
  As Mohan and Ravi together can finish the work in 7.5 or 15/2 days, their 1 day work=2/15.
  So, 1/x + 1/(x-8)= 2/15
  (x-8+x)/[x(x-8)] =2/15
  x^2 -23x+60 =0
  (x-3)(x-20)=0
  as x can't be 3, x=20,
• 8 years agoHelpfull: Yes(21) No(0)
• Ans 20.
  
  suppose the work to be done is to shift 120 chairs (multiple of 7.5 and 8)
  Then in 1 day mohan n ravi together shifts 120/7.5 = 16 chairs.
  
  now if we take option 1 i.e if Ravi takes 15 days to finish it alone , it means in 1 day he is shifting 120/15 = 8 chairs.
  i.e Mohan shifting 16-8=8 chairs. Now it mohan shifts 8 chairs he alone will take 15 days.
  20-15 !=8. so this is not correct ans.
  
  now take option 3 i.e 20 days n repeat the above procedure.
• 7 years agoHelpfull: Yes(4) No(3)
• Ans-20
  Suppose ravi will finish work in x days
  Mohan take 8 days less than ravi so Mohan can complete in x-8 days
  
  So
  1/x+1/x-8=7.5
  After solution u will get it x=20
  
• 7 years agoHelpfull: Yes(4) No(1)
• ans is (3) 20 days.
• 7 years agoHelpfull: Yes(0) No(1)