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Working simultaneously and independently at an identical con

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Working simultaneously and independently at an identical con

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Working simultaneously and independently at an identical constant rate, 4 machines of a certain type can produce a total of x units of product P in 6 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?

A. 24
B. 18
C. 16
D. 12
E. 8

OA B

Source: GMAT Prep

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BTGmoderatorDC wrote:
Working simultaneously and independently at an identical constant rate, 4 machines of a certain type can produce a total of x units of product P in 6 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?

A. 24
B. 18
C. 16
D. 12
E. 8

OA B

Source: GMAT Prep
We are given that 4 machines can complete x units in 6 days. Thus, the rate of the 4 machines is x/6.

Now, we need to determine the number of machines needed to produce a rate of 3x/4. To calculate that number of machines, we can use the following proportion in which the value in each numerator is the number of machines and the value in each denominator is the corresponding rate of those machines. We can let n = the number of machines needed:

4/(x/6) = n/(3x/4)

24/x = 4n/3x

72x = 4nx

18 = n

Alternate Solution:

If 4 machines can produce a total of x units of product P in 6 days, then 12 machines can produce 3x units of product P in 6 days. To find the number of machines needed to produce 3x units in 4 days, let’s set up an inverse proportion, denoting the number of machines needed by n. The proportion is: “12 machines is to 6 days as n machines is to 4 days”:

12 x 6 = 4 x n

n = 3 x 6 = 18

Answer: B

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scott@targettestprep.com



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We have x units by 4 machines in 6 days

\(\Rightarrow \, x\) units in 24 machine days
\(\Rightarrow\, 3x\) units in 72 machine days

Therefore machine required \(= \frac{72}{4} = 18\)

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GMAT/MBA Expert

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BTGmoderatorDC wrote:
Working simultaneously and independently at an identical constant rate, 4 machines of a certain type can produce a total of x units of product P in 6 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?

A. 24
B. 18
C. 16
D. 12
E. 8
Use the following equation:

(machines)(time) / output = (machines)(time) / output

In the equation above:
Machines and time are INVERSELY PROPORTIONAL.
As the number of machines increases, the amount of time required to produce the same output decreases.
Machines and output are DIRECTLY PROPORTIONAL.
As the number of machines increases, the amount of output also increases.
Time and output are also DIRECTLY PROPORTIONAL.
As the amount of time increases, the amount of output also increases.

Let x=1.
Since 4 machines take 6 days to produce x=1 unit, and we want to know how many machines are required to produce 3x=3 units in 4 days, we get:
(4 machines)(6 days)/(1 unit) = (n machines)(4 days)/(3 units)
24 = 4n/3
72 = 4n
18 = n

The correct answer is B.

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GMAT/MBA Expert

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BTGmoderatorDC wrote:
Working simultaneously and independently at an identical constant rate, 4 machines of a certain type can produce a total of x units of product P in 6 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?

A. 24
B. 18
C. 16
D. 12
E. 8

OA B

Source: GMAT Prep
Let's assign a nice value to x (a value that will work well with all of the numbers 3, 4 and 6.

Let's say x = 24

GIVEN: 4 machines make x units in 6 days
This means 4 machines make 24 units in 6 days
So, 4 machines make 4 units in 1 day [if you divide the work time by 6, the output is also divided by 6]
So, 1 machine makes 1 unit in 1 day [if you divide the number of machines by 4, the output is also divided by 4]

From here, we can answer the question How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?
If x = 24, 3x = 72
Our goal is to make 72 units in 4 days.

So, 1 machine makes 4 units in 4 days [if you multiply the work time by 4, the output is also multiplied by 4]
So, 18 machines make 72 units in 4 days [if you multiply the number of machines by 18, the output is also multiplied by 18]

Answer: B

Cheers,
Brent

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Brent Hanneson – Creator of GMATPrepNow.com
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