3 machines individually can do a certain job in 4,5 & 6 hrs respectively.What is the greatest part of the job that can be done in one hour by two of the machines working together at their respective rates?
A) 11/30
B) 9/20
C) 3/5
D) 11/15
E) 5/6
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greatest part of work (man hours)
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kishokbabu
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LalaB
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I surely canVanshika21 wrote:Hi,LalaB wrote:(4+5)/4*5=9/20
Can you pls explain why you took 4 and 5 and not 5 and 6?
U are asked about "the greatest part"
so lets take 5 and 6 hours
then u will have
(5+6)/5*6=11/30
please note, that 11/30 <9/20
since u r asked about the greatest part, u better get the least hours
,i.e. 4 and 5hope it is clear
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Since we must MAXIMIZE the amount of work produced, the SLOWEST machine cannot be used.kishokbabu wrote:3 machines individually can do a certain job in 4,5 & 6 hrs respectively.What is the greatest part of the job that can be done in one hour by two of the machines working together at their respective rates?
A) 11/30
B) 9/20
C) 3/5
D) 11/15
E) 5/6
The fastest machine takes 4 hours to complete the job; the next fastest machine takes 5 hours.
Let the job = 20 units.
Rate for the fastest machine = w/t = 20/4 = 5 units per hour.
Rate for the next fastest machine = w/t = 20/5 = 4 units per hour.
(Work produced by the 2 machines in 1 hour)/(Total job) = (5+4)/20 = 9/20.
The correct answer is B.
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Here we have to compare work fastest machine with other two.
Work completed A in 1 hr is 1/4,
Work completed B in 1 hr is 1/5
Work completed C in 1 hr is 1/6
A+B = 9/20 ~ 1/2.22
A+C = 10/24 = 5/12 ~ 1/2.4
So A+B takes 2.22 hrs to complete 1 work, so can complete more work.
So answer B
Work completed A in 1 hr is 1/4,
Work completed B in 1 hr is 1/5
Work completed C in 1 hr is 1/6
A+B = 9/20 ~ 1/2.22
A+C = 10/24 = 5/12 ~ 1/2.4
So A+B takes 2.22 hrs to complete 1 work, so can complete more work.
So answer B
