A and B can complete work together in 5 days. If A works at twice his speed and B at half of his speed, this work can be finished in 4 days. How many days would it take for A alone to complete the job?

• A one day work=1/x
  B one day work=1/y
  
  (A+B)=1/x+1/y=1/5
  (x+y)/xy=1/5
  5(x+y)=xy -------(1)
  
  if A worked at twice =2/x
  B worked at half=1/2y
  
  2/x+1/2y=1/4
  (4y+x)/2xy=1/4
  8y+2x=xy-----(2)
  
  substitute (2) in (1)
  
  8y+2x=5x+5y
  3y=3x
  
  y=x that means number days worked by A alone is equal to B alone
  
  substitute in (1)
  
  1/x+1/x=1/5
  2/x=1/5
  A=10 days
  
  B=10days
• 4 years agoHelpfull: Yes(1) No(0)
• ans: 1
  
  
  x+y=5
  
  2x+.5y=4 or 4x+y=8
  
  4x+y-x-y=8-5=3 or 3x=3
  
  => x=1
• 5 years agoHelpfull: Yes(0) No(2)