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

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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