A and B together can complete a work in 12 days. A alone can complete it in 20 days. If B does the work only for half a day daily, then in how many days A and B together will complete the work?
A. 10 days B. 11 days
C. 15 days D. 20 days

• see ,
  here given that A and B can do the work in 12 days
  so A+B 1 day work = 1/12 unit.................................(1)
  also given that , a alone can finish the work in 20 days
  therefore
  A 1 day work = 1/20 unit........................................(2)
  using 1 and 2
  we get,
  B's 1 day work =1/12 - 1/20
  =1/30..............................(3)
  ---> b can do the complete work in 30 days
  now according to statement
  if b does the work only half a day then it takes double days (i.e. 60) to complete the work
  so now B 1 day work = 1/60.
  also we know
  A 1 day work = 1/20
  now,
  A+B 1 day work = 1/60 + 1/20
  = 4/60
  = 1/15 unit work
  hence ,
  A and B together will complete the work in " 15 DAYS " (answer)
  
• 12 years agoHelpfull: Yes(66) No(7)
• A+B=1/12
  A=1/20
  B=1/12-1/20=1/30
  A+B/2=1/20+1/(2*30)=1/15
• 9 years agoHelpfull: Yes(16) No(0)
• Ur time is around 2 mint not 20 mint, follow this method
  
  A completes the work in 20 days = 5% work done by A per day
  A+B takes 12 days = 8.33% work done by both per day
  Work done by B alone = 8.33-5 = 3.33 % per day
  If B works half a day then contribution by B per day = 1.6%
  Work done by both per day = 5+1.6 = 6.6 %
  total days = 100/6.6 around 15 days
• 9 years agoHelpfull: Yes(4) No(4)
• ans is 15 days
• 9 years agoHelpfull: Yes(2) No(0)
• a*b/(a+b)=12
  20*x/(20+x)=12
  20x-12x=240
  x=30
  i.e b=60
  20*60/(20+60)=15
  ans is 15
• 7 years agoHelpfull: Yes(1) No(0)
• here given that A and B can do the work in 12 days
  so A+B 1 day work = 1/12 unit.................................(1)
  also given that , a alone can finish the work in 20 days
  therefore
  A 1 day work = 1/20 unit........................................(2)
  using 1 and 2
  we get,
  B's 1 day work =1/12 - 1/20
  =1/30..............................(3)
  ---> b can do the complete work in 30 days
  now according to statement
  if b does the work only half a day then it takes double days (i.e. 60) to complete the work
  so now B 1 day work = 1/60.
  also we know
  A 1 day work = 1/20
  now,
  A+B 1 day work = 1/60 + 1/20
  = 4/60
  = 1/15 unit work
  hence ,
  A and B together will complete the work in " 15 DAYS " (answer)
• 6 years agoHelpfull: Yes(1) No(1)
• 1/A + 1/B= 1/12
  1/B + 1/C= 1/15
  
  therefore,1/A - 1/C = 1/60
  1/C=1/30-1/60 => 1/60
  
  B = 20 days
  C = 60 days
  1/A+1/B+1/C=1/30+1/60+1/20=1/10
  ans. 10
• 8 years agoHelpfull: Yes(0) No(4)
• C- 15days
• 7 years agoHelpfull: Yes(0) No(0)