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# If it takes 70 workers 3 hours to disassemble the exhibition rides at

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Math Expert
Joined: 02 Sep 2009
Posts: 64227
If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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26 Nov 2014, 06:41
00:00

Difficulty:

5% (low)

Question Stats:

79% (00:56) correct 21% (01:12) wrong based on 156 sessions

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Tough and Tricky questions: Work/Rate Problems.

If it takes 70 workers 3 hours to disassemble the exhibition rides at a small amusement park, how many hours would it take 30 workers to do this same job?

A. 40/3
B. 11
C. 7
D. 7/3
E. 9/7

Kudos for a correct solution.

Source: Chili Hot GMAT

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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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26 Nov 2014, 10:11
1
Bunuel wrote:

Tough and Tricky questions: Work/Rate Problems.

If it takes 70 workers 3 hours to disassemble the exhibition rides at a small amusement park, how many hours would it take 30 workers to do this same job?

A. 40/3
B. 11
C. 7
D. 7/3
E. 9/7

Kudos for a correct solution.

Source: Chili Hot GMAT

let w= 210 units.
thus rate of each worker = $$\frac{210}{3.70}$$ = $$1$$ $$unit$$

hence, time taken by 30 workers to complete 210 units =$$\frac{210}{30}$$ = $$7$$ $$days$$
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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26 Nov 2014, 10:32
1
Choice C

It takes 70 workers 3 hours to finish the task. This means we can set up the expression 70 * 1/x = 1/3 hours. Solving for x, yields 210 hours or the time it would take each worker on their own. So, for 3 workers, it takes 30*1/x = 1/T (hours). Since x=210 hours, we can solve for T to be 7 hours.
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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26 Nov 2014, 11:41
2
1
1
70 Workers = 3 hours then,
1 Worker = 3*70 Hours
30 Workers = (3*70) /(30) = 7 Answer.
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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26 Nov 2014, 20:02
1
Work = worker * time = 70 * 3 =210.
210 = 30 * t => t =7.

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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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26 Nov 2014, 20:15
3
1

Rate of one worker $$= \frac{1}{70*3} = \frac{1}{210}$$

Rate of 30 workers $$= 30 * \frac{1}{210} = \frac{1}{7}$$

Time taken = 7 Hours
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Posts: 64227
Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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27 Nov 2014, 06:31
Bunuel wrote:

Tough and Tricky questions: Work/Rate Problems.

If it takes 70 workers 3 hours to disassemble the exhibition rides at a small amusement park, how many hours would it take 30 workers to do this same job?

A. 40/3
B. 11
C. 7
D. 7/3
E. 9/7

Kudos for a correct solution.

Source: Chili Hot GMAT

Yes, the correct answer is C.
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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30 Aug 2016, 22:10
Bunuel wrote:

Tough and Tricky questions: Work/Rate Problems.

If it takes 70 workers 3 hours to disassemble the exhibition rides at a small amusement park, how many hours would it take 30 workers to do this same job?

A. 40/3
B. 11
C. 7
D. 7/3
E. 9/7

Kudos for a correct solution.

Source: Chili Hot GMAT

CONCEPT: $$\frac{(Machine_Power * Time)}{Work} = Constant$$
i.e. $$\frac{(M_1 * T_1)}{W_1} = \frac{(M_2 * T_2)}{W_2}$$

i.e. $$\frac{(70 * 3)}{1} = \frac{(30 * T_2)}{1}$$

i.e. $$T_2 = 7$$

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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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31 Aug 2016, 10:49
t*30*1/210=1
t=7 hours
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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17 Jun 2018, 18:34
Why does setting up a proportion lead you to the wrong answer?

(70 workers/3 hours) = (30 workers/X hours)
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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18 Jun 2018, 04:05
1
mdcf wrote:
Why does setting up a proportion lead you to the wrong answer?

(70 workers/3 hours) = (30 workers/X hours)

Hi mdcf

70 workers take 3 hours - Work done is 210 worker hours
30 workers take X hours - Work done is 30X worker hours

Here, we can equate the work done by 70 machines and 30 machines, 30X = 210
Solving for X, we get X = $$\frac{210}{30} = 7$$

What you were trying to equate was the work done in an hour(which is not the same)

Hope this helps you!
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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20 Jun 2018, 16:25
Bunuel wrote:

Tough and Tricky questions: Work/Rate Problems.

If it takes 70 workers 3 hours to disassemble the exhibition rides at a small amusement park, how many hours would it take 30 workers to do this same job?

A. 40/3
B. 11
C. 7
D. 7/3
E. 9/7

The rate of 70 workers is 1/3;if we let x = the rate of 30 workers, then we can set up the proportion

70/(1/3) = 30/x

70x = 30(1/3)

70x = 10

x = 1/7

Since the rate of the 30 workers is 1/7, the time it takes to do the job is 1/(1/7) = 7 hours.

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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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20 Jun 2018, 20:55
Bunuel wrote:

Tough and Tricky questions: Work/Rate Problems.

If it takes 70 workers 3 hours to disassemble the exhibition rides at a small amusement park, how many hours would it take 30 workers to do this same job?

A. 40/3
B. 11
C. 7
D. 7/3
E. 9/7

Kudos for a correct solution.

Source: Chili Hot GMAT

The job requires 70 * 3 = 210 man hours

Hence 30 workers will finish the job in = 210/30 = 7 hours.

Thanks,
GyM
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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20 Jun 2018, 22:41

Solution

Given:

• 70 workers take 3 hours to disassemble the exhibition rides.

To find:

• How many hours will 30 workers take to disassemble the exhibition rides.

Approach and Working:

70 workers take 3 hours to disassemble the exhibition rides.
• Thus, complete work takes 70*3= 210 worker-hours to complete the work.

Now, if 30 workers do the same work then,
• They will take 210/30= 7 hours to do the same work.

Hence, the correct answer is option C.

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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at  [#permalink]

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10 Aug 2019, 16:33
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Re: If it takes 70 workers 3 hours to disassemble the exhibition rides at   [#permalink] 10 Aug 2019, 16:33