51.
A certain number of persons can dig a trench 100 m long, 50 m broad and 10 m
deep in 10 days. The same number of persons can dig another trench 20 m broad
and 15 m deep in 30 days. The length of the second trench is:
[A]400
m
[B]500 m
[C]
800 m
[D]
900 m
Answer : B
Explanation :
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Let
the required length be x metres.
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More
breadth, Less length (Indirect Proportion)
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More
depth, Less length (Indirect Proportion)
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More
days, More length (Direct Proportion)
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Breadth
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20
: 50
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Depth
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15
: 10
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Days
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10
: 30
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::
100 : x
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20
x 15 x 10 x x = 50 x 10 x 30 x 100
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x =
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(50 x 10 x 30 x 100)
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(20 x 15 x 10)
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