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Joined: 20 Feb 2017
Posts: 2506
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Machine A currently takes x hours to complete a certain job. Machine B
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04 Apr 2021, 22:34
04 Apr 2021, 22:34
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52% (03:07) correct
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Machine A currently takes x hours to complete a certain job. Machine B currently takes y hours to complete the same job. If x=4y, by what percent will x have to decrease so that A and B together can complete the job in 3y/8 hours ?
A. 15%
B. 25%
C. 30%
D. 62,5%
E. 85%
A. 15%
B. 25%
C. 30%
D. 62,5%
E. 85%
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Machine A currently takes x hours to complete a certain job. Machine B
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06 Apr 2021, 03:51
06 Apr 2021, 03:51
2
GeminiHeat wrote:
Machine A currently takes x hours to complete a certain job. Machine B currently takes y hours to complete the same job. If x=4y, by what percent will x have to decrease so that A and B together can complete the job in 3y/8 hours ?
A. 15%
B. 25%
C. 30%
D. 62,5%
E. 85%
A. 15%
B. 25%
C. 30%
D. 62,5%
E. 85%
Let \(y = 1\)
Then \(x = 4\)
Now \(A\) and \(B\) together require \(\frac{3y}{8}\) hours to finish the job, Let us assume that \(A\) now requires \(z\) hours for the same.
i.e. \(\frac{zy}{(z + y)} = \frac{3y}{8}\)
\(\frac{z}{(z + 1)} = \frac{3}{8}\)
\(8z = 3z + 3\)
\(z = \frac{3}{5}\) hours
% Change = \(\frac{(4 - 0.60)}{4}(100) = 85\)%
Hence, option E
Re: Machine A currently takes x hours to complete a certain job. Machine B
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06 Apr 2021, 10:34
06 Apr 2021, 10:34
Hi Karun,
Can you please explain how you came up with the formula zy/(z+y)? I don't understand the logic behind it.
Can you please explain how you came up with the formula zy/(z+y)? I don't understand the logic behind it.
