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Twelve engineers can complete a task in 7 Hours.12 engineers started t

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Manager
Joined: 13 Jun 2012
Posts: 189
Location: United States
WE: Supply Chain Management (Computer Hardware)
Twelve engineers can complete a task in 7 Hours.12 engineers started t  [#permalink]

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02 Jan 2018, 14:32
1
5
00:00

Difficulty:

85% (hard)

Question Stats:

53% (03:10) correct 47% (03:18) wrong based on 72 sessions

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Twelve engineers can complete a task in 7 Hours.12 engineers started the task at 10 AM but starting from 1PM, One engineer leaves every Hour,At what time the task gets completed?

1.5.30pm
2.6.00 pm
3.6.30 pm
4.7.00 pm
5.7.30 pm
Math Expert
Joined: 02 Aug 2009
Posts: 6956
Twelve engineers can complete a task in 7 Hours.12 engineers started t  [#permalink]

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02 Jan 2018, 20:29
Turkish wrote:
Twelve engineers can complete a task in 7 Hours.12 engineers started the task at 10 AM but starting from 1PM, One engineer leaves every Hour,At what time the task gets completed?

1.5.30pm
2.6.00 pm
3.6.30 pm
4.7.00 pm
5.7.30 pm

HI...

every Q can be made easy by a bit of logic..

so let's make it easy by counting the man hour required.. $$12*7=84$$..
all 12 work for three hours together, so they cover $$12*3=36$$ hrs
remaining = $$84-36=48$$
now each hour 1 person moves out
cancel out hours per hour ..
$$48-11-10-9-8-7 = 3$$ hours remaining after 5 hours
people remaining that time = 6 and work required 3 man hours, so these 6 will do it in $$\frac{3}{6} = \frac{1}{2}$$ hour
therefore time after 1 is 5+1/2 or 6:30 pm
C
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3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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Intern
Joined: 15 Jan 2018
Posts: 1
Twelve engineers can complete a task in 7 Hours.12 engineers started t  [#permalink]

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15 Jan 2018, 03:35
Hi,

We can solve this question easily, if we assume the work in terms of the number of workers and the time taken to do the work.
• Let us assume that 1 engineer can complete 1 unit of work in an hour.
o Thus, 12 engineers can complete 12 units of work in one hour.
• According to the question they are working for 7 hours, thus the total work done by them would be = 12*7 = 84 units
• Starting from 10 am, they worked together until 1 pm. This is equal to 3 hours of work.
o So total work done = 12*3 = 36 units.
o Remaining work = 84 – 36 = 48 units
• Since one person is leaving after 1 pm, the work done per hour after 1pm is the following:
o From 1-2: 11 units. Remaining work = 37 units
o From 2-3: 10 units. Remaining work = 27 units
o From 3-4: 9 units. Remaining work = 18 units
o From 4-5: 8 units. Remaining work = 10 units
o From 5-6: 7 units. Remaining work = 3 units
• Remaining work = 3 units and 6 workers who can do 6 units in one hour.
o Hence, time taken to complete the last 3 units of the task = 3/6 hours = 1/2 hour = 30 mins
• So, the work will be completed by 6:30 pm.

Regards,
John
Twelve engineers can complete a task in 7 Hours.12 engineers started t &nbs [#permalink] 15 Jan 2018, 03:35
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