A is twice efficient than B. A and B can both work together to complete a work in 7 days. Then find in how many days A alone can complete the work?

• ans is 10.5
  gn:
  A+B=(1/7)
  A=2B
  =>B=1/21
  A=2/21
  =>A take (21/2)=10.5 days to complete the work.
• 11 years agoHelpfull: Yes(25) No(2)
• assume B works in a day = w
  so A works in a day= 2w
  as given both works for 7 days so total work done is =7(w+2w)=21w
  
  Now if A alone want to complete work of 21w
  so time taken by A is = 21w/2w => 10 and 1/2 days
• 11 years agoHelpfull: Yes(14) No(0)
• give that,
  A=2B
  noe A andB can do a work in 7 days
  then take their one days work as
  A+B=1/7
  substitute A=2B then
  B=1/81
  so A=2/81
  therefore A's one day work=2/81
  he can complete that work with in 81/2 days
  
• 11 years agoHelpfull: Yes(3) No(15)
• since a=2b then,
  time taken to complete work by a and b is (1/2b+1/b)=1/7 then we get b=21/2
  and since a=2b so a=2(21/2)= 21 would be the answer.
• 11 years agoHelpfull: Yes(3) No(3)
• (A+B)'s one day work=1/7
  divide 1/7 in ratio 2:1
  A's one day work=(1/7)*(2/3)=2/21
  hence A can do work in 21/2=10.5 days
  
• 11 years agoHelpfull: Yes(1) No(0)
• (1/x)+ (2/x)=(1/7)
  get value of x=21
  then x/2=10.5 which is answer
• 9 years agoHelpfull: Yes(0) No(0)
• 7(A+B)=1
  7(2B+B)=1
  B=1/21
  hence , A=2B=2*1/21=2/21
  now, (2/21)*x=1
  x=21/2=10.5 days
• 6 years agoHelpfull: Yes(0) No(0)