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# 24 computer hackers can scan and infect 10 computers in 5 hours. If th

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Intern
Joined: 11 Jul 2016
Posts: 25
Location: Thailand
GMAT 1: 700 Q48 V38
24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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22 Jun 2017, 19:04
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Difficulty:

55% (hard)

Question Stats:

82% (01:56) correct 18% (02:27) wrong based on 120 sessions

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24 computer hackers can scan and infect 10 computers in 5 hours. If this group of hackers wants to scan and infect 20 computers in 8 hours, how many new computers hackers do they need to recruit and join their team in order to accomplish this task, assuming all hackers work at the same rate?

A) 0
B) 6
C) 8
D) 10
E) 16

Source- Barron Gmat

I got a
B, but apparently it is D
but isn't correct. Please kindly explain. Thank you
Intern
Joined: 05 Sep 2016
Posts: 3
Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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22 Jun 2017, 19:25
1
Here the quantum of work is getting doubled so we have to equate man-hour accordingly.Therefore the equation would be:

24*5/10={(24+x)*8}/20.

Solving this will give x=6

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Posts: 1977
Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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23 Jun 2017, 11:27
1
ssr300 wrote:
24 computer hackers can scan and infect 10 computers in 5 hours. If this group of hackers wants to scan and infect 20 computers in 8 hours, how many new computers hackers do they need to recruit and join their team in order to accomplish this task, assuming all hackers work at the same rate?

A) 0
B) 6
C) 8
D) 10
E) 16

Source- Barron Gmat

I got a
B, but apparently it is D
but isn't correct. Please kindly explain. Thank you

I think you're right, and Barron is not.

Work = (Number of workers) x (individual Rate) x (Time), or

W = (N)(R)(T)

So the individual rate of the original 24 hackers (N) who take 5 hours (T) to hack 10 computers (W) is

10/(5*24) = $$\frac{10}{120}$$ or R = $$\frac{1}{12}$$

At that rate, to hack 20 computers in 8 hours, the number of hackers needed would be

$$(\frac{1}{12}$$)*(8)*(N)= 20

$$\frac{2}{3}$$N = 20

N = 30. There are already 24. The hackers need 6 more people.

I think the answer is B.
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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23 Jun 2017, 11:42
Great Question and my answer is similar to ksingh16

24 * 5/10 = ((24+x)*8)/20

Simplifying this we get:

x = 6

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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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23 Jun 2017, 11:43
ssr300 wrote:
24 computer hackers can scan and infect 10 computers in 5 hours. If this group of hackers wants to scan and infect 20 computers in 8 hours, how many new computers hackers do they need to recruit and join their team in order to accomplish this task, assuming all hackers work at the same rate?

A) 0
B) 6
C) 8
D) 10
E) 16

Source- Barron Gmat

I got a
B, but apparently it is D
but isn't correct. Please kindly explain. Thank you

[b]ssr300 Request you to EDIT the OA, as it is not D, it is B

[/b]
_________________

"Nothing in this world can take the place of persistence. Talent will not: nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not: the world is full of educated derelicts. Persistence and determination alone are omnipotent."

Best AWA Template: https://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html#p470475

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Joined: 26 Feb 2016
Posts: 3131
Location: India
GPA: 3.12
Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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23 Jun 2017, 11:44
Let the number of units of work done(to hack one system) is 120 units.
Since 24 hackers, infect 10 computers, they do 1200 units of work. This work takes these hackers 5 hours.
So, in essence, 1 hacker does 1200 / (5*24) which is 10 units of work/hour

Now we have to infect 20 computers, making the units of work to do 2400 units.
It has been given that there are 24 hackers, and we are asked to find
how many additional hackers are required to pull this work in 8 hours.

No of hackers = 2400/ (8*10) = 30
Since they have 24 hackers, they will need to recruit 6 additional hackers to pull this job off(Option B)
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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29 Jun 2017, 03:13
I too agree with everyone here that OA should be B. No wonder that only a few answered it right.

Bunuel, could you shed some light on this question please?
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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29 Jun 2017, 03:25
utkarshthapak wrote:
I too agree with everyone here that OA should be B. No wonder that only a few answered it right.

Bunuel, could you shed some light on this question please?

_____________________
Edited the OA. Thank you.
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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29 Jun 2017, 08:28
I solved it in a different way... please tell me if my way of reasoning is not flawed...

24 Hackers works at a Rate of 10/5 --> R=2

X Hackers works at a Rate of 20/8 --> R=5/2

So I set up a proportion:

(2/1)/24 = (5/2)/X
1/12 = 5/2x

Cross multiplying we get X=30 and Number Of Additional Hackers would be 30-24 = 6 thus B
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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29 Jun 2017, 08:47
1
ssr300 wrote:
24 computer hackers can scan and infect 10 computers in 5 hours. If this group of hackers wants to scan and infect 20 computers in 8 hours, how many new computers hackers do they need to recruit and join their team in order to accomplish this task, assuming all hackers work at the same rate?

A) 0
B) 6
C) 8
D) 10
E) 16

Use Shortcut formula -

$$\frac{M_1*T_1}{W_2} = \frac{M_2*T_2}{W_1}$$

So, $$\frac{24*5}{20} = \frac{(24 + m)*8}{24}$$

Or, $$6 = \frac{(24 + m)}{3}$$

Or, $$18 = 24 + m$$

So, $$m = 6$$

Thus, the answer will be (B)
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Manager
Joined: 06 Sep 2016
Posts: 136
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GMAT 1: 650 Q43 V37
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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29 Jun 2017, 08:55
Abhishek009 wrote:
ssr300 wrote:
24 computer hackers can scan and infect 10 computers in 5 hours. If this group of hackers wants to scan and infect 20 computers in 8 hours, how many new computers hackers do they need to recruit and join their team in order to accomplish this task, assuming all hackers work at the same rate?

A) 0
B) 6
C) 8
D) 10
E) 16

Use Shortcut formula -

$$\frac{M_1*T_1}{W_2} = \frac{M_2*T_2}{W_1}$$

So, $$\frac{24*5}{20} = \frac{(24 + m)*8}{24}$$

Or, $$6 = \frac{(24 + m)}{3}$$

Or, $$18 = 24 + m$$

So, $$m = 6$$

Thus, the answer will be (B)

Can you please explain me how it work or give me a link to the detailed explanation about how to use it? Thanks
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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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29 Jun 2017, 09:14
1
MvArrow wrote:
Can you please explain me how it work or give me a link to the detailed explanation about how to use it? Thanks

https://gmatclub.com/forum/understandin ... 69681.html

Hope the discussion here, helps..

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Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th  [#permalink]

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05 Jul 2018, 16:50
ssr300 wrote:
24 computer hackers can scan and infect 10 computers in 5 hours. If this group of hackers wants to scan and infect 20 computers in 8 hours, how many new computers hackers do they need to recruit and join their team in order to accomplish this task, assuming all hackers work at the same rate?

A) 0
B) 6
C) 8
D) 10
E) 16

We are given that the rate of 24 computer hackers is 10/5 = 2.

We need the new rate to be 20/8 = 5/2. We can let x = the number of computer hackers needed to achieve that rate and create the following proportion:

24/2 = x/(5/2)

12 = x/(5/2)

12 = 2x/5

60 = 2x

x = 30

So, the number of new hackers needed is 30 - 24 = 6.

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Re: 24 computer hackers can scan and infect 10 computers in 5 hours. If th &nbs [#permalink] 05 Jul 2018, 16:50
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