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13 Jul 2020, 06:49
Kudos
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
56% (01:52) correct
44%
(02:17)
wrong
based on 18
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Machine A can a do a job 50% faster than machine b. If together they can complete a job in 4 hours. How many hours it take machine A to complete the job alone?
A.5
B.7
C.8
D.10
E.11
A.5
B.7
C.8
D.10
E.11
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13 Jul 2020, 08:05
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Are you sure the answer choices you provided are correct?
This is what I got, but I might be doing something wrong since this answer isn't in the answer choices.
Machine A's rate = \(\frac{3}{2}\)r
Machine B's rate = r
(\(\frac{3}{2}\)r + r)(4) = 1
10r = 1
r = \(\frac{1}{10}\)
So the rate of Machine B is \(\frac{1}{10}\). This means the rate of Machine A is \(\frac{3}{20}\).
Time it takes for Machine A to complete the job alone:
\(\frac{3}{20}\)t = 1
t = 20/3
This is what I got, but I might be doing something wrong since this answer isn't in the answer choices.
Machine A's rate = \(\frac{3}{2}\)r
Machine B's rate = r
(\(\frac{3}{2}\)r + r)(4) = 1
10r = 1
r = \(\frac{1}{10}\)
So the rate of Machine B is \(\frac{1}{10}\). This means the rate of Machine A is \(\frac{3}{20}\).
Time it takes for Machine A to complete the job alone:
\(\frac{3}{20}\)t = 1
t = 20/3
yashikaaggarwal
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13 Jul 2020, 08:09
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If A if 1.5 times faster than B then it takes less time than B
A takes x hours
B takes 1.5x hours
1/x is A's rate per day
1/1.5x is B's rate per day
they take 4 days together
(1/x)(4)+(1/1.5x)(4)=1 (job finished)
(4/x)+(4/1.5x)=1
multiply both sides by 1.5x
(1.5)(4)+4=1.5x
6+4=1.5x
10=1.5x
X = 6.66 or 7 hours
Answer is B
Bunuel kindly Edit OA.
A takes x hours
B takes 1.5x hours
1/x is A's rate per day
1/1.5x is B's rate per day
they take 4 days together
(1/x)(4)+(1/1.5x)(4)=1 (job finished)
(4/x)+(4/1.5x)=1
multiply both sides by 1.5x
(1.5)(4)+4=1.5x
6+4=1.5x
10=1.5x
X = 6.66 or 7 hours
Answer is B
Bunuel kindly Edit OA.
