It takes 6 engineers 10 hours to build and program a new server from Direct Computer, with each working at the same rate. If six engineers start to build the server at 11:00 AM, and one engineer per hour is added beginning at 5:00 PM, at what time will the server be complete?

1 7:00 PM
2 7:20 PM
3 6:40 PM
4 8:00 PM

• 8 PM.
  
  6*10 = 60 man hours are reqd for the job.
  If six engineers start to build the server at 11:00 AM, 6*6 = 36 man hour job is done by 5 PM.
  24 man hour job is left which is completed in 3 hrs by 7,8,9 engineer in next 3 hrs.
  
  so job will be completed by 8 PM.
• 13 years agoHelpfull: Yes(25) No(3)
• 6 engineer = 1/10 work
  1 engineer = 1/60 work
  till 5PM, 6 engineers and 6 hours, so work done is 6/10
  so the work remaining is : 4/10
  now 1 person added, so the work efficiency now is 7/60
  4/10 - 7/60 = 17/60 (at 6PM)
  now 1 person added, so the work efficiency now is 8/60
  17/60 - 8/60 = 9/60 (at 7PM)
  now 1 person added, so the work efficiency now is 9/60
  9/60 - 9/60 = 0 (at 8PM) ~~~ WORK DONE..
• 13 years agoHelpfull: Yes(16) No(3)
• 1 engineer= 1/60th of work
  till 5 pm work done= 3/5
  work left= 2/5
  in next every hour work done increases by 1/60
  so after 6 pm work left = 2/5-7/60 = 17/60
  after 7pm work left = 17/60-8/60 = 9/60
  after 8pm work left = 9/60-9/60 = 000
  so work will be done at 8 pm
• 13 years agoHelpfull: Yes(2) No(0)