A does a work in 20 days. A did for 28 days. Then b came. They together take 76 days to complete the 7 job. Find howmany days B complete a work.

• time for A to do one job IN 1 DAY= 1/20
  time for A to do one job IN 28 DAY= 28/20
  time for B to do one job IN 1 DAY= 1/B (LET)
  SO,EQUATION A/Q:
  28/20 + 76/20 + 76/B = 7
  multiply by 20B BOTH SIDE:
  1520 = 36B
  B = 42.22 days to do one job alone
• 12 years agoHelpfull: Yes(18) No(1)
• In 20 days A completes 1 job. So,in 28 days A completes 1 2/5 job. Job left to be done is 7-(1 2/5) = 5 3/5 job. A and B work together for 76-28 = 48 days and complete 5 3/5 job. Let B completes work in B days i.e., rate of B is 1/B. A's rate is 1/20.
  (1/20 + 1/B) * 48 = 5 3/5
  => 240 + 12B = 28B
  => 16B = 240
  => B = 15 days
• 10 years agoHelpfull: Yes(14) No(4)
• the ques is wrong ..if it takes A to complete the work in 20 days then in 28 days work will have already been completed..
• 11 years agoHelpfull: Yes(13) No(7)
• http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Rate-of-work-word-problems.faq.question.625647.html
• 8 years agoHelpfull: Yes(2) No(0)
• does a work in 20 days. A worked for 28 days.
  Then B came. Working together, they take 76 days to complete 7 jobs.
  Find how many days it takes B to complete a work.
  :
  let b = time for B to do one job by himself
  let one completed job = 1
  :
  
  %28%2828%2B76%29%29%2F20 + 76%2Fb = 7
  104%2F20 + 76%2Fb = 7
  multiply by 20b
  104b + 20(76) = 20b(7)
  104b + 1520 = 140b
  1520 = 140b - 104b
  1520 = 36b
  b = 1520%2F36
  b = 42.22 days to do one job alone
• 8 years agoHelpfull: Yes(1) No(0)