At this rate, how many bolts could 4 such machines produce..

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Running at the same constant rate, "a" identical machines can produce a total of 120 bolts per minute. At this rate, how many bolts could 4 such machines produce in 5 minutes?

(A) a/6
(B) a/600
(C) 150/a
(D) 480/a
(E) 2,400/a

The OA is E.

I am very confuse here. Who is "a"? and why is E?

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by Brent@GMATPrepNow » Tue Sep 12, 2017 12:35 pm
Vincen wrote:Running at the same constant rate, "a" identical machines can produce a total of 120 bolts per minute. At this rate, how many bolts could 4 such machines produce in 5 minutes?

(A) a/6
(B) a/600
(C) 150/a
(D) 480/a
(E) 2,400/a

The OA is E.
The "a" represents a variable.
The question would be clearer if it read as follows:
Running at the same constant rate, k identical machines can produce a total of 120 bolts per minute. At this rate, how many bolts could 4 such machines produce in 5 minutes?

(A) k/6
(B) k/600
(C) 150/k
(D) 480/k
(E) 2,400/k
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Vincen wrote:Running at the same constant rate, "a" identical machines can produce a total of 120 bolts per minute. At this rate, how many bolts could 4 such machines produce in 5 minutes?

(A) a/6
(B) a/600
(C) 150/a
(D) 480/a
(E) 2,400/a

The OA is E.
We can solve this question using equivalent ratios.

Given: a identical machines produce a total of 120 bolts per ONE minute
So, a identical machines produce a total of 600 bolts per FIVE minutes

How many bolts could 4 such machines produce in 5 minutes?
Let x = the number of bolts 4 machines can produce in 5 minutes
We get: a/600 = 4/x
Cross multiply to get: ax = (600)(4)
Simplify to get: ax = 2400
Divide both sides by a to get: x = 2400/a
Answer: E

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by GMATGuruNY » Tue Sep 12, 2017 2:36 pm
Vincen wrote:Running at the same constant rate, "a" identical machines can produce a total of 120 bolts per minute. At this rate, how many bolts could 4 such machines produce in 5 minutes?

(A) a/6
(B) a/600
(C) 150/a
(D) 480/a
(E) 2,400/a
Let a=1, implying that 1 machine produces 120 bolts per minute.
Since 1 machine produces 120 bolts per minute, the rate for 4 machines = 4*120 = 480 bolts per minute.
At a rate of 480 bolts per minute, the number of bolts produced by the 4 machines in 5 minutes = rt = 480*5 = 2400 bolts. This is our target.

Now plug a=1 into the answer choices to see which yield the target value of 2400.
Only E works:
2400/a = 2400/1 = 2400.

The correct answer is E.
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by Scott@TargetTestPrep » Wed Sep 20, 2017 2:43 pm
Vincen wrote:Running at the same constant rate, "a" identical machines can produce a total of 120 bolts per minute. At this rate, how many bolts could 4 such machines produce in 5 minutes?

(A) a/6
(B) a/600
(C) 150/a
(D) 480/a
(E) 2,400/a
We are given that the rate of a machines is 120. Thus, the rate of 4 machines is:

a/120 = 4/x

ax = 480

x = 480/a

Since the rate of 4 machines is 480/a bolts per minute, 4 machines can produce 480/a * 5 = 2400/a bolts in 5 minutes.

Answer: E

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