A and B each working alone can do a work in 15 days and 25 days respectively. They started the work together, but B left after some time and A finished the remaining work in 7 days. After how many days from the start did B leave?

• A can finish work in 1 day = 1/15
  B can finish work in 1 day = 1/25
  Both A & B can finish work in 1 day = 1/15 + 1/25 = 8/75
  Part of the work A alone finished in 7 days = 7/15
  Part of work A & B together finished = 8/15
  So A & B together finished the 8/15 of the work in = (8/15)/(8/75)= 5 days
  So B left from the start of the work after 5 days.
• 12 years agoHelpfull: Yes(16) No(1)
• total work= LCM(15,25)=75 units work
  A can do 15 days work= 75 units work
  ===> 1 days work= 75/15=5 units work
  
  B can do 25 days work= 75 units work
  ===> 1 days work= 75/25=3 units work
  
  Both A and B can do 1 day work= 5+3=8 units work.
  let B left after x days
  Complted work = workdone by both= 8x
  remaining work work done my A= 7*5
  Completed work + Remaining work = Total work
  ===> 8x+7*5=75
  ===> x=5 days
  
• 12 years agoHelpfull: Yes(6) No(3)
• A completes 100/15 = 6.66 %
  B '''''''' 100/25 = 4%
  A work 7 days so it completes 6.66*7 = 44.42%
  Remaining work done by A+B ( 6.66% + 4% = 10.66) which is 56 % approx
  so for these work AB takes 10.66*5 = 53% so Ans = 5 days
  
• 11 years agoHelpfull: Yes(4) No(3)
• great soln rakesh
• 12 years agoHelpfull: Yes(2) No(2)