A can do a piece of work in 5 hours, B in 9 hours and C in 15 hours. if C could work with them for 1 hour only, the time taken by A and B together to complete the work is.
[A] 8 hours
[C] 5 hours
[B] 3 hours
[D] 2 hours

• answer = 2 hours
  
• 10 years agoHelpfull: Yes(17) No(6)
• A work in 1 hour=1/5
  b work in 1 hour =1/9
  c work in 1 hour = 1/15
  
  a+b+c work in 1 hour = 1/5 + 1/9+ 1/15=17/45
  c's work in 1 hour= 1/15
  after 1 hour remaining work = 1-1/15=14/15
  a+b work in 1 hour= 1/5+ 1/9 = 14/45
  remaining work by a+b in 1 hour = 14/45 * 15/14 = 1/3
  so a and b work together to complete this work in 3 hours.
• 10 years agoHelpfull: Yes(5) No(6)
• C one hour work is 1/15
  i.e 1/15 of the work completed by c
  remaining 14/15 work can be completed by A and B
  
  A+B one day work is 1/9+1/15=14/45
  
• 10 years agoHelpfull: Yes(1) No(11)
• A can do a work in 1 hour is 9 parts
  B can do a work in 1hour is 5 parts
  c can do a work in 1 hour is 3 parts
  
  total work is 45 parts
  
  so, if c could work with them for 1 hour is = 9+5+3 = 17 parts completed
  remaining parts A and B completed. their 1 hour work is 14 parts
  
  so, 17(1hr)+14(1 hr)+14(1 hr)
  
  remaining work is complete in 2hrs
• 6 years agoHelpfull: Yes(1) No(0)