A completes 80% of a work in 20 days. Then B also joins and A and B together finish the remaining work in 3 days. How long does it need for B if he alone completes the work?

• A completes 4/5 work in 20 days
  so he can complete the whole work in (5*20)/4 = 25 days
  A one day work is 1/25 ------ (1)
  A & B Complete the 1/5 of work in 3 days
  They Both can complete the work in 5*3 = 15 days
  One day work of A nd B is 1/15 ----- (2)
  B one day work is 1/x;
  1/x= 1/15-1/25
  1/x = 2/75
  x = 75/2 ==>> 37.5
  b can complete whole work in 37(1/2) days
• 9 years agoHelpfull: Yes(32) No(0)
• Efficiency of A=80/20=4%
  Efficiency of A+B=20/3=6.66%
  so,
  Efficiency of B=6.66-4=2.66
  No of days need by B to complete the work alone=100/2.66=37.59
  =38 days approx
• 9 years agoHelpfull: Yes(14) No(1)
• 
  For all friends..
  work = days
  
  for A:
  80% work = 20 days
  4/5 work = 20 days
  cross mul
  1 work = 5/4 * 20 days
  1 work = 25 days
  A's 25 days = 1 work ----------------------------->1
  
  A+B remain work done in 3 days
  total work = 1
  80% work = 4/5
  100% work = 1
  100% - 80% = 1 - 4/5 = 1/5
  
  for A+B:
  work = days
  1/5 work = 3 days
  cross mul
  1 work = 15 days
  dat is
  
  A+B's 15 days = 1 work --------------------------->2
  
  now we know A's and A+B's work
  now find B's work
  apply A's in A+B's
  A+B 1 Days= 1/15 works
  A's 1 days = 1/25 works---->from 1..
  
  1/25 + B = 1/15 works
  B's days = 1/15 - 1/25 Works
  B's days= 2/75 works
  we have to calc works
  cross mul
  B's work = 75/2 days = 37 1/2 days
  Rahul said: (Sat, Jan 29, 2011 08:45:53 AM)
  
  @ baskar: thanks dude
  Rajendra said: (Tue, Feb 8, 2011 01:54:11 AM)
  
  A does 80% in 20 days..so
  A does 100% in 25 days..
  A's 1 day work=1/25
  A+B does 20% in 3 days..so
  A+B does 100% in 15 days
  A+B's 1 day work=1/15
  1/25+B=1/15
  B=1/15-1/25
  B,s 1 day work=2/75
  so B,s work=75/2 i.e 37 1/2 days..
• 9 years agoHelpfull: Yes(2) No(0)
• B completes the work in 37.5 days
  
• 9 years agoHelpfull: Yes(1) No(0)
• 100% done in 25 days by A .
  and 100% done in 15 days by B.
  so 5-5/3=37.5
  
• 9 years agoHelpfull: Yes(0) No(1)
• B alone do the work in xy/x-y days
  15*25/10=37.5 days
• 9 years agoHelpfull: Yes(0) No(0)
• 15/22 b alone can do it
• 9 years agoHelpfull: Yes(0) No(0)
• since A can do 80% work in 20 days
  then in 1 day it can do work= 80%/20=4/100
  let B in 1 day ,work=1/x
  so we can say,
  20(4/100)+3(4/100 + 1/x)=1
  4/5+12/100+3/x=1
  x=37.5
  thus ,B takes 37.5 days
• 9 years agoHelpfull: Yes(0) No(0)
• 37.5 days is answer
  
  23/25 +3/x =1
  
  
  x=37.5
• 9 years agoHelpfull: Yes(0) No(0)