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?

• let total work is 100 unit .
  
  A can do 80 unit in 20 days ....so he can do 4 unit in 1 days .
  
  now A has finished 80 units so remaining work is 20 unit
  
  so , 20 unit work takes 3 days time to complete in which A will do 12 unit
  
  (since A do 4 unit/days )
  
  thus ,B do 8 unit in 3 days
  
  and total work is 100 unit so B will take (3/8)*100 = 37.5 days to complete total work
• 9 years agoHelpfull: Yes(39) No(2)
• 37 1/2 days
  
  A alone can complete the work in (20/80)*100= 25 days
  As work completed by A is 80%=80/100=4/5, remaining work= 1/5
  If B alone can complete the work in 'x' days, then
  3 days work of A & B= 3*[(1/25)+(1/x)]= 1/5
  1/x=2/75 or x=75/2 =37.5
• 9 years agoHelpfull: Yes(10) No(3)
• ANSWER==> 37.5 days
  A can complete the whole work = (20/80)*100=25 days
  remaining work= 20%= 1/5
  B complete the works = X days(say)
  the [(1/25+1/X)*3]=1/5
  so X=37.5 days
• 9 years agoHelpfull: Yes(6) No(2)
• Work done by A in 20 days = 80/100 = 8/10 = 4/5
  
  Work done by A in 1 day = (4/5) / 20 = 4/100 = 1/25 --- (1)
  
  Work done by A and B in 3 days = 20/100 = 1/5 (Because remaining 20% is done in 3 days by A and B)
  
  Work done by A and B in 1 day = 1/15 ---(2)
  
  Work done by B in 1 day = 1/15 – 1/25 = 2/75
  
  => B can complete the work in 75/2 days = 37 (1/2) days
• 8 years agoHelpfull: Yes(6) No(0)
• Work done by A in 20 days = 80/100 = 8/10 = 4/5
  
  Work done by A in 1 day = (4/5) / 20 = 4/100 = 1/25 --- (1)
  
  Work done by A and B in 3 days = 20/100 = 1/5 (Because remaining 20% is done in 3 days by A and B)
  
  Work done by A and B in 1 day = 1/15 ---(2)
  
  Work done by B in 1 day = 1/15-1/25 = 2/75
  
  => B can complete the work in 75/2 days = 37 (1/2) days
• 9 years agoHelpfull: Yes(4) No(0)
• 80% of work = 80/100 = 4/5 in 20 days. therefore in one day A does 4/(20*5) = 1/25. the remaining work to be done is 20% hence 20/100 = 1/5. Therefore ((1/25)+(1/x))3 = 1/5, which gives x = 75/2 = 37.5
• 9 years agoHelpfull: Yes(2) No(1)
• A => 80% -20 days
  4% - 1 day
  100% - 25 days
  
  A+B => 20 % -3 days
  100 % -15 days
  LCM(25,15)= 75
  
  A =>75/25 =3 UNITS/DAY
  A+B =>75/15 =5 UNITS/DAY
  B =2 UNITS/DAY
  B =75/2 =37 1/2
• 8 years agoHelpfull: Yes(2) No(0)
• A completes =80/20=4% of work
  remaining work = 20%
  A+B=20/3=6.6667% work
  A+B-A=6.6667-4=2.6667
  100% work done in 2.6667
  100/2.6667=37.5 or 37 1/2
  
  
• 8 years agoHelpfull: Yes(1) No(0)
• 7 1/2 days.
• 9 years agoHelpfull: Yes(0) No(3)
• 37.5 days
  
• 9 years agoHelpfull: Yes(0) No(0)
• A=0.8/20
  (.8/20)+B=.2/3
  B=(2/30)-(8/200)
  B=(2/75)
  B=(1/37.5)
  
  SO B WIIL COMPLETE THE WORK IN 37.5DAYS
• 9 years agoHelpfull: Yes(0) No(0)
• A--20days =80/100 work
  A--1day=(80/100)*1/20==1/25
  A+B--3days=1/5work
  A+B--1day=(1/5)*1/3==1/15
  B's 1day work =A+B-A=1/15-1/25==2/75
  Therefore B can complete the work in 75/2 or 37.5 days
• 6 years agoHelpfull: Yes(0) No(0)
• A can completes the work in 20 days so the efficiency will be 4%(80/20=4)
  now the remaining works is 20 %
  A+B efficiency =20/3
  A+B=20/3
  4+B=20/3
  B=8/3
  now b alone can complete the work=100/8/3=37.5
• 4 years agoHelpfull: Yes(0) No(0)