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Each of two generators produces energy at a constant rate, but the two

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Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 26 Nov 2018, 23:05
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Each of two generators produces energy at a constant rate, but the two rates are different. One of the generators produces n units of energy in 4 hours, and the other generator produces the same amount of energy in half the time. What fraction of n units of energy will be produced by both generators if they work simultaneously for 40 minutes?

A. 3/8
B. 1/2
C. 5/8
D. 3/4
E. 7/8

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Re: Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 27 Nov 2018, 02:34
imo - b - 1.5 hrs

total hrs = 100
a's speed - 100/4 = 25
b's speed - 100/2 - 50

total speed - 75/hr

in 40 mins - 2/3*75 = 50.

50/100= 1/2 answer - b
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Re: Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 27 Nov 2018, 07:51
Bunuel wrote:
Each of two generators produces energy at a constant rate, but the two rates are different. One of the generators produces n units of energy in 4 hours, and the other generator produces the same amount of energy in half the time. What fraction of n units of energy will be produced by both generators if they work simultaneously for 40 minutes?

A. 3/8
B. 1/2
C. 5/8
D. 3/4
E. 7/8



(n/4+n/2) * (40 /60)

3n/4*(2/3)
n/2 option B
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Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 27 Nov 2018, 08:41
Bunuel wrote:
Each of two generators produces energy at a constant rate, but the two rates are different. One of the generators produces n units of energy in 4 hours, and the other generator produces the same amount of energy in half the time. What fraction of n units of energy will be produced by both generators if they work simultaneously for 40 minutes?

A. 3/8
B. 1/2
C. 5/8
D. 3/4
E. 7/8



i converted hours to minutes so 4 hours 240 minuts and 2 hours 120 minutes

\(\frac{n}{240}\) +\(\frac{n}{120}\) = \(\frac{1}{40}\)

\(\frac{3n}{240} = \frac{1}{40}\) cross multiply

\(n = \frac{240}{120}\)

\(n = 120\) hence half i.e ---> \(\frac{1}{2}\)

B

chetan2u is my solution correct ? :) please let me know :grin:
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Re: Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 27 Nov 2018, 08:45
Archit3110 wrote:
Bunuel wrote:
Each of two generators produces energy at a constant rate, but the two rates are different. One of the generators produces n units of energy in 4 hours, and the other generator produces the same amount of energy in half the time. What fraction of n units of energy will be produced by both generators if they work simultaneously for 40 minutes?

A. 3/8
B. 1/2
C. 5/8
D. 3/4
E. 7/8



(n/4+n/2) * (40 /60)

3n/4*(2/3)
n/2 option B



hello Archit3110 are you multiplying total work done by part of work done ? :)
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Re: Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 27 Nov 2018, 08:50
1
dave13 wrote:
Archit3110 wrote:
Bunuel wrote:
Each of two generators produces energy at a constant rate, but the two rates are different. One of the generators produces n units of energy in 4 hours, and the other generator produces the same amount of energy in half the time. What fraction of n units of energy will be produced by both generators if they work simultaneously for 40 minutes?

A. 3/8
B. 1/2
C. 5/8
D. 3/4
E. 7/8



(n/4+n/2) * (40 /60)

3n/4*(2/3)
n/2 option B



hello Archit3110 are you multiplying total work done by part of work done ? :)

dave13

Actually I skipped a step or two and did straight the calculation.

rate of generator @ 4hours : n/4 & @ 2 hours : n/2
combined rate (n/4)+(n/2)
3n/4
so in 40 mins i.e 40/60: 2/3 hours it would produce 2/3 * 3n/4 i.e n/2 which means 1/2 of n ...

hope this helps
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Re: Each of two generators produces energy at a constant rate, but the two  [#permalink]

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New post 27 Nov 2018, 21:14
1
dave13 wrote:
Bunuel wrote:
Each of two generators produces energy at a constant rate, but the two rates are different. One of the generators produces n units of energy in 4 hours, and the other generator produces the same amount of energy in half the time. What fraction of n units of energy will be produced by both generators if they work simultaneously for 40 minutes?

A. 3/8
B. 1/2
C. 5/8
D. 3/4
E. 7/8



i converted hours to minutes so 4 hours 240 minuts and 2 hours 120 minutes

\(\frac{n}{240}\) +\(\frac{n}{120}\) = \(\frac{1}{40}\)

\(\frac{3n}{240} = \frac{1}{40}\) cross multiply

\(n = \frac{240}{120}\)

\(n = 120\) hence half i.e ---> \(\frac{1}{2}\)

B

chetan2u is my solution correct ? :) please let me know :grin:



Hi dave13,
You are solution is correct uptil a point and required an extra term to make sense..
What does \(\frac{n}{240}\) +\(\frac{n}{120}\) mean. It means addition of per minute work of both generators.
This should be equal to x/40, if they are making X in 40 minutes when combined.
While \(\frac{1}{40}\) means that both make 1 in 40 minutes..

So the equation would be \(\frac{n}{240}\) +\(\frac{n}{120}\) = \(\frac{x}{40}\)....
And x=n/2 so HALF of n...
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3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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Re: Each of two generators produces energy at a constant rate, but the two &nbs [#permalink] 27 Nov 2018, 21:14
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