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It takes $6$ technicians a total of $10$ hours to build a new server from Direct Computer, with each working at the same rate. If six technicians start to build the server at $11$ am and one technician per hour is added beginning at $5$ pm, at what time will be the server be complete?
1. $6:40$ pm
2. $7:00$ pm
3. $7:20$ pm
4. $8:00$ pm

Option D at 8pm

6 technicians take 10hrs to build a server or to complete = a work

1 technician cn work in 1 hr is= 1/10*6 work

Work done by 6 technicians in 6hr (11 am to 5pm)= 6*6/10*6 work

= 6/10 Work

Remaining work 1-6/10= 4/10 work

For next 1 hr one technician is added ( 6pm)

So work done by 7 technician 1 hr = 7*1/10*6 work = 7/60 work

Remaining Work= 4/10 -7/60= 17/60work

For next 1 hr one technician is added ( 7pm)

So work done by 8 technician 1 hr = 8*1/10*6 work = 8/60 work

Remaining Work= 17/60 -8/60= 9/60work

For next 1 hr one technician is added ( 8pm)

So work done by 9 technician 1 hr = 9/10*6 work = 9/60 work

= Remaining Work 9/60 - 9/60=0 Remaining work

Server will br completed at 8 pm
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