Three machines, K, M, and P, working simultaneously and : GMAT Data Sufficiency (DS)
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Three machines, K, M, and P, working simultaneously and

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Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes.
(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes.
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Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

Say k, m, and p are the numbers of minutes machines K, M, and P take, respectively, to complete the task. Then we have that \(\frac{1}{k}+\frac{1}{m}+\frac{1}{p}=\frac{1}{24}\).

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes --> \(\frac{1}{m}+\frac{1}{p}=\frac{1}{36}\), thus \(\frac{1}{k}+\frac{1}{36}=\frac{1}{24}\) --> we can find the value of \(k\). Sufficient.

(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes --> \(\frac{1}{k}+\frac{1}{p}=\frac{1}{48}\). The value of k cannot be determined from the data we have. Not sufficient.

Answer: A.
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 04 Mar 2013, 01:57
Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes.
RATE :(K + M + P) - RATE : (M+P) = RATE : K. SUFFICIENT
(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes.
RATE :(K + M + P) - RATE : (K+P) = RATE : M. NOT SUFFICIENT
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 28 Nov 2013, 05:29
Bunuel wrote:
Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

Say k, m, and p are the numbers of minutes machines K, M, and P take, respectively, to complete the task. Then we have that \(\frac{1}{k}+\frac{1}{m}+\frac{1}{p}=\frac{1}{24}\).

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes --> \(\frac{1}{m}+\frac{1}{p}=\frac{1}{36}\), thus \(\frac{1}{k}+\frac{1}{36}=\frac{1}{24}\) --> we can find the value of \(k\). Sufficient.

(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes --> \(\frac{1}{k}+\frac{1}{p}=\frac{1}{48}\). The value of k cannot be determined from the data we have. Not sufficient.

Answer: A.



I approached this pbm a little differently. Pls. Explain where I am going wrong...is it OK to reason this way?

Let Rk, Rm and Rp be the rates for the machines K,M and P respectively.
Then 1/Rk +1/Rm+1/Rp = 24

St 1 gives ---> 1/Rm + 1/Rp = 36

So, we get 1/Rk + 36 = 24.

Solving, 1/Rk = 24-36=-12

Why am I getting a negative value?
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 29 Nov 2013, 09:12
audiogal101 wrote:
Bunuel wrote:
Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

Say k, m, and p are the numbers of minutes machines K, M, and P take, respectively, to complete the task. Then we have that \(\frac{1}{k}+\frac{1}{m}+\frac{1}{p}=\frac{1}{24}\).

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes --> \(\frac{1}{m}+\frac{1}{p}=\frac{1}{36}\), thus \(\frac{1}{k}+\frac{1}{36}=\frac{1}{24}\) --> we can find the value of \(k\). Sufficient.

(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes --> \(\frac{1}{k}+\frac{1}{p}=\frac{1}{48}\). The value of k cannot be determined from the data we have. Not sufficient.

Answer: A.



I approached this pbm a little differently. Pls. Explain where I am going wrong...is it OK to reason this way?

Let Rk, Rm and Rp be the rates for the machines K,M and P respectively.
Then 1/Rk +1/Rm+1/Rp = 24

St 1 gives ---> 1/Rm + 1/Rp = 36

So, we get 1/Rk + 36 = 24.

Solving, 1/Rk = 24-36=-12

Why am I getting a negative value?


1/Rk, 1/Rm, and 1/Rp are the numbers of minutes machines K, M, and P take to complete the task alone. Each must be greater than the time needed for three machines to complete a certain task together (24 minutes), thus 1/Rk +1/Rm+1/Rp = 24 is not right. The same for 1/Rm + 1/Rp = 36.

Hope it's clear.
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PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 29 Nov 2013, 21:35
Bunuel wrote:
audiogal101 wrote:
Bunuel wrote:
Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

Say k, m, and p are the numbers of minutes machines K, M, and P take, respectively, to complete the task. Then we have that \(\frac{1}{k}+\frac{1}{m}+\frac{1}{p}=\frac{1}{24}\).

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes --> \(\frac{1}{m}+\frac{1}{p}=\frac{1}{36}\), thus \(\frac{1}{k}+\frac{1}{36}=\frac{1}{24}\) --> we can find the value of \(k\). Sufficient.

(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes --> \(\frac{1}{k}+\frac{1}{p}=\frac{1}{48}\). The value of k cannot be determined from the data we have. Not sufficient.

Answer: A.



I approached this pbm a little differently. Pls. Explain where I am going wrong...is it OK to reason this way?

Let Rk, Rm and Rp be the rates for the machines K,M and P respectively.
Then 1/Rk +1/Rm+1/Rp = 24

St 1 gives ---> 1/Rm + 1/Rp = 36

So, we get 1/Rk + 36 = 24.

Solving, 1/Rk = 24-36=-12

Why am I getting a negative value?


1/Rk, 1/Rm, and 1/Rp are the numbers of minutes machines K, M, and P take to complete the task alone. Each must be greater than the time needed for three machines to complete a certain task together (24 minutes), thus 1/Rk +1/Rm+1/Rp = 24 is not right. The same for 1/Rm + 1/Rp = 36.

Hope it's clear.


Got it. So would it be correct to say that 1/ (Rk+Rm+Rp) = 24? (since the denominator has combined rate now)?
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 18 May 2014, 09:47
st 1:

After rephrase :

n = (3^n)/9

No idea about "t". so Insufficient

St 2 :
t = 3^n

Insufficient

Combining st1 & st 2

t= 9n

Plug in few numbers to cross check is n a factor of t??

let n = 2 ; t = 9 *2 = 18

yes n is a factor of t

n= 7; t = 9*7 = 63

yes n is a factor of t

IMO C
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 19 May 2014, 01:59
gmatkum wrote:
st 1:

After rephrase :

n = (3^n)/9

No idea about "t". so Insufficient

St 2 :
t = 3^n

Insufficient

Combining st1 & st 2

t= 9n

Plug in few numbers to cross check is n a factor of t??

let n = 2 ; t = 9 *2 = 18

yes n is a factor of t

n= 7; t = 9*7 = 63

yes n is a factor of t

IMO C


I think this post is about some other question. :-D
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Collection of Questions:
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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New post 05 Apr 2015, 07:22
Bunuel, does wording seem confusing for you, too? When it writes independently it seems they work separately with the same rate.
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Re: Three machines, K, M, and P, working simultaneously and [#permalink]

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Re: Three machines, K, M, and P, working simultaneously and   [#permalink] 18 Apr 2016, 20:47
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