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Bunuel
Working together at their respective constant rates, robot A and robot B polish 88 pounds of gemstones in 6 minutes. If robot A’s rate of polishing is 3/5 that of robot B, how many minutes would it take robot A alone to polish 165 pounds of gemstones?

(A) 15.75
(B) 18
(C) 18.75
(D) 27.5
(E) 30

Since Robot A works at \(\frac{3}{5}(60\)%) the rate at which Robot B works, together they do work of \(1.6(1+.6)\) robots.

1.6 robots polish 88 pounds in 6 minutes. In 6 minutes, Robot A(0.6 robot) polishes \(\frac{88}{1.6}*0.6\) or 33 pounds of gemstones.

Therefore, it will take Robot A (\(\frac{165}{33} = 5\)) 6 minute intervals = 30(Option E) minutes to polish 165 pounds of gemstones.
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Bunuel
Working together at their respective constant rates, robot A and robot B polish 88 pounds of gemstones in 6 minutes. If robot A’s rate of polishing is 3/5 that of robot B, how many minutes would it take robot A alone to polish 165 pounds of gemstones?

(A) 15.75
(B) 18
(C) 18.75
(D) 27.5
(E) 30
Let , Efficiency of Robot B = 5e
So, Efficiency of Robot A = 3e

Combined efficiency of A and B is 8e = \(\frac{88}{6}\) pounds/min

Or, e = \(\frac{11}{6}\) pounds/min

So, Efficiency of A = \(\frac{33}{6}\) pound/min

Thus, Time taken for robot A to polish 165 gemstones is \(\frac{165*6}{33}\) = 30 minutes, Answer must be (E)
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Soln: Working together - A+B = 88 in 6 mins.

A = 3/5 B

3/5B+B = 88

3B+5B = 88 * 5

8B = 440 ; B = 55 i.e - B polishes 55 pounds in 6 mins , Rate of B = 55 / 6 per min.

A = 3/5 B

A = 3/5 * 55/6 = 11/2 pound/min

W = Rate * Time

Time = Work / Rate

Time for A = 165 / (11/2) = 330/11 = 30 Mins.

Thanks.
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Given: A+B rate * 6 minutes = 88 lbs
B rate = B, A rate = (3/5)*B
Question: 165 lbs / 3/5(B) = ? minutes

1) A+B rate * 1 minute = 88/6 lb

2) 88/6 = A+(3/5)A ---> 8/5A
A = 88/6 * 5/8 --> 55/6
55/6*3/5 = 11/2, rate of (3/5)A per minute

3) 165/11/2 = 30 minutes, E
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I like using a work chart: Work = rate * time

So... 88 gemstones = 6 minutes * 88/6

Now, since 88/6 is our combined rate, we need to set it equal to (A + B), aka (B + 3/5B): 88/6 = 8/5B

88 * 5/8 = 6B

55/6 = B (rate of)

Now solve for A (rate of)...

A = 55/6 * 3/5 = 11/2

Rate of Machine A is 11/2.

Now, Machine A working alone can polish 165 gemstones at a rate of 11/2 in: 165 = 11/2A (time of A)

15 * 2 = 30 minutes
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88 = (A+B)1/10
880 = A+5/3A
880 = 8/3A
330 = A

165 = At
165/330 = t
t = 1/2 hour = 30min
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Bunuel
Working together at their respective constant rates, robot A and robot B polish 88 pounds of gemstones in 6 minutes. If robot A’s rate of polishing is 3/5 that of robot B, how many minutes would it take robot A alone to polish 165 pounds of gemstones?

(A) 15.75
(B) 18
(C) 18.75
(D) 27.5
(E) 30


R*T=W

For A+B
R*6min = 88 Pounds
Implies R=88/6 pounds/min

Let Rate for B be x
Therefore, Rate for A = 3/5x

Rate of A+Rate of B = Rate of (A+B)
3/5x + x = 88/6
Solving for x
x= 55/6
Implying Rate of A = 3/5x = 11/2 pounds/min

Interpretation
A completes 11/2 pounds in 1 min
Therefore, it will complete 165 pounds of work in 165/(11/2) min = 30 min.Option E
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The video solution of the question shall be as :
https://www.loom.com/share/8d60aafabac645e5962a014083206304
Bunuel
Working together at their respective constant rates, robot A and robot B polish 88 pounds of gemstones in 6 minutes. If robot A’s rate of polishing is 3/5 that of robot B, how many minutes would it take robot A alone to polish 165 pounds of gemstones?

(A) 15.75
(B) 18
(C) 18.75
(D) 27.5
(E) 30
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Working together at their respective constant rates, robot A and robot B polish 88 pounds of gemstones in 6 minutes. If robot A’s rate of polishing is 3/5 that of robot B, how many minutes would it take robot A alone to polish 165 pounds of gemstones?

(A) 15.75
(B) 18
(C) 18.75
(D) 27.5
(E) 30

__________________________

Let A, B be the rate of Robot A and B, respectively.

Total work = work rate/time x time

(A+B) x 6(min) = 88(pounds) — (1)
A = 3B/5 — (2)

(1) + (2),
B = 55/6
A = 33/6

Now, the question is asking A(work rate of A) x time = 165(pounds).
Replace A with 33/6,
Time = 6/33 x 165
Time = 30

Therefore, the answer is E.
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Can someone explain why the combined work formula doesn't work here? I understand your methodology, but keep getting 18 using that formula. Thanks!
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Kindly write what do you mean by "combined work formula"


dsmaier
Can someone explain why the combined work formula doesn't work here? I understand your methodology, but keep getting 18 using that formula. Thanks!
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