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Intern  Joined: 05 Oct 2011
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The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

(1) The delivery cost for the order totalled more than \$30.00.
(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.
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GMAT 1: 780 Q51 V48 GRE 1: Q800 V740 Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Simple one.

Using (1), the total is to be more than \$30, which can be the case if n is greater than or less than 24. For instance, when n=22, the total cost is \$31, but when n=25, the total cost is \$34, which are both greater than \$30. Insufficient.
Using (2), we are given that [10 + (n-1)]/n = 1.36
=> n= 25, which is greater than 24. Sufficient.

The answer is (B).
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Intern  Joined: 22 Mar 2011
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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1
(1) only tells us n >= 21; not sufficient by itself
(2) tells us [10+n-1]/n = 1.36; which will lead to a definitive answer and therefore is sufficient by itself

Thus, B.
Manager  Joined: 28 Jul 2011
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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2
Vote for B

\$10 - first chair
\$1 - additional

order n

is n>24? i.e. cost should be least 10(1) + 1(23) = \$33 for 24 chairs

(A) delivery cost > 30

data not sufficient

(B)

S=An
10+(n-1) = 1.36n
9 + n= 1.36n
9 = 0.36n
9/.36 = n
25 = n

Sufficient
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

awesome as you have rephrased the statement,.

We could think also in this way: 1 chair cost 10 and the others 1 more \$. for 24 chairs we have a total of 33 \$. so we could say: is total cost more than 33\$ ??? is correct bunuel ??

also is unclear (n-1) in the formula above is not : Tot= 10 + 1*N ??????? N is the number of chair.....

thanks Moderator.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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2
1
carcass wrote:
Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

awesome as you have rephrased the statement,.

We could think also in this way: 1 chair cost 10 and the others 1 more \$. for 24 chairs we have a total of 33 \$. so we could say: is total cost more than 33\$ ??? is correct bunuel ??

also is unclear (n-1) in the formula above is not : Tot= 10 + 1*N ??????? N is the number of chair.....

thanks Moderator.

The cost of the first chair is \$10 and \$1 for each additional chair.

So, for n chairs one chair goes for \$10 and the rest n-1 chairs go for \$1 each, total \$10+\$1*(n-1)=9+n.

Hope it's clear.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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I.E. 15 chairs: the first one is 10 \$, 14 chairs are 1 \$ each. our (n-1) is the cost of 1\$ for (15-1).

Totally stupid I'm.

Thanks Bunuel.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

I am not so good at translating words to numbers, could you post some similar problems to practice the skill?
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Stiv wrote:
Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

I am not so good at translating words to numbers, could you post some similar problems to practice the skill?

search.php?search_id=tag&tag_id=183 for DS
search.php?search_id=tag&tag_id=56 for PS

Hope this helps.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Vidhi1 wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n>24?

1. The delivery cost for the order totaled more than \$30.00
2. The average (arithmetic mean) delivery cost of the n chairs was \$1.36

So, now we can see that, for statement 1, the question is how much more than \$30.00? At \$31.00, n<24, while at, say \$300.00, n>24.

For statement 2, from the average and the information in the stem, we can calculate n: (10 + (n-1))/n = 1.36, so n = 25.

So, the correct response is B.
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GMAT 1: 710 Q47 V40 Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Bunuel wrote:
carcass wrote:
Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

awesome as you have rephrased the statement,.

We could think also in this way: 1 chair cost 10 and the others 1 more \$. for 24 chairs we have a total of 33 \$. so we could say: is total cost more than 33\$ ??? is correct bunuel ??

also is unclear (n-1) in the formula above is not : Tot= 10 + 1*N ??????? N is the number of chair.....

thanks Moderator.

The cost of the first chair is \$10 and \$1 for each additional chair.

So, for n chairs one chair goes for \$10 and the rest n-1 chairs go for \$1 each, total \$10+\$1*(n-1)=9+n.

Hope it's clear.

]
worndering where 9+n came from. I was plugging in numbers to find averages - 11, 6, etc...crazy
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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amenon55 wrote:
Bunuel wrote:
carcass wrote:

awesome as you have rephrased the statement,.

We could think also in this way: 1 chair cost 10 and the others 1 more \$. for 24 chairs we have a total of 33 \$. so we could say: is total cost more than 33\$ ??? is correct bunuel ??

also is unclear (n-1) in the formula above is not : Tot= 10 + 1*N ??????? N is the number of chair.....

thanks Moderator.

The cost of the first chair is \$10 and \$1 for each additional chair.

So, for n chairs one chair goes for \$10 and the rest n-1 chairs go for \$1 each, total \$10+\$1*(n-1)=9+n.

Hope it's clear.

]
worndering where 9+n came from. I was plugging in numbers to find averages - 11, 6, etc...crazy

The cost of the first chair is \$10 and \$1 for each additional chair.

So, for n chairs one chair goes for \$10 and the rest n-1 chairs go for \$1 each, total \$10+\$1*(n-1)=9+n.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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ruturajp wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

(1) The delivery cost for the order totalled more than \$30.00.
(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36.

Given : \$10 for first chair and \$1 for each additional Chair

i.e. Total Cost of n chairs = 10 + (n-1)*1

Question : Is n > 24 ?

Statement 1: The delivery cost for the order totalled more than \$30.00.
10 + (n-1)*1 > 30
i.e. n > 21
NOT SUFFICIENT

Statement 2: The average (arithmetic mean) delivery cost of the n chairs was \$1.36.
[10 + (n-1)*1]/n = 1.36
i.e. 1.36n = 10 + (n-1)
i.e. 0.36n = 9
i.e. n = 25
SUFFICIENT

Answer: Option B
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GMAT 1: 630 Q48 V29 Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

Hi Bunuel
If stmnt 2 would be The average (arithmetic mean) delivery cost of the n chairs was greater than \$1.36
then we get n<25 --> in that case, number of chairs could be 24,23,1, 10 in any case answer will be NO, n>24? NO hence sufficient
am I right?
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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anupamadw wrote:
Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

Hi Bunuel
If stmnt 2 would be The average (arithmetic mean) delivery cost of the n chairs was greater than \$1.36
then we get n<25 --> in that case, number of chairs could be 24,23,1, 10 in any case answer will be NO, n>24? NO hence sufficient
am I right?

Yes, if it were (9+n)/n>1.36, it still would be sufficient.
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and equations ensures a solution.

The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

(1) The delivery cost for the order totalled more than \$30.00.
(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36.

From the original condition, using cost:c gives us c=10+(n-1)1=9+n and thus we have 2 variable (c,n) and 1 equation (c=9+n). Since we need to match the number of variables and equations, we need 1 more equation and we have 1 each in 1) and 2). Therefore D is likely the answer.

In case of 1), c>30, 9+n>30, n>21 therefore the condition is not sufficient(if the range of que includes the range of con then the condition is sufficient)
In case of 2), c=1.36n=9+n, 1.36n-n=9, 0.36n=9, n=25>24 the answer is yes. The condition is sufficient and therefore the answer is B
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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GyanOne wrote:
Simple one.

Using (1), the total is to be more than \$30, which can be the case if n is greater than or less than 24. For instance, when n=22, the total cost is \$31, but when n=25, the total cost is \$34, which are both greater than \$30. Insufficient.
Using (2), we are given that [10 + (n-1)]/n = 1.36
=> n= 25, which is greater than 24. Sufficient.

The answer is (B).

Hi

Is this a+(n-1)d?

where d is 1?
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Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Bunuel wrote:
The cost of delivery for an order of desk chairs was \$10.00 for the first chair, and \$1.00 for each additional chair in the order. If an office manager placed an order for n desk chairs, is n > 24 ?

According to the rule given in the stem the cost of delivery for n chairs is \$10+\$1*(n-1)=9+n.

(1) The delivery cost for the order totalled more than \$30.00 --> 9+n>30 --> n>21, so n may or may not be more than 24. not sufficient.

(2) The average (arithmetic mean) delivery cost of the n chairs was \$1.36 --> (average cost)=(total cost)/(# of chairs)=(9+n)/n. We are told that (9+n)/n=1.36 --> we can find the exact numerical value of n. Sufficient.

Answer: B.

Hi
Great Explanation Bunuel.
For (2) I tried using the conventional formula for the Sum of n terms of an AP.
i.e. n/2(2*(1st term)+(n-1)*(common difference))
Here the 1st term is 10 and the common difference was 1.

the final equation which I got was

10+((n-1) /2)=1.36

Here I am getting the value of n as negative.
So I chose E.

Please tell me where I am wrong.

Thanks in Advance
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GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: The cost of delivery for an order of desk chairs was \$10.00 for the fi  [#permalink]

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Hi All,

We're told that the cost of delivery for an order of desk chairs was \$10.00 for the first chaircand \$1.00 for each additional chair in the order. We're asked if an office manager placed an order for N desk chairs, is N > 24. This is a YES/NO question. This DS question is a nice example of what's called "a question BEHIND the question."; this idea of finding another way to view the question usually occurs a few times on Test Day and makes those particular questions easier to answer.

Since we know what 24 chairs would cost (\$10 for the 1st, \$1 for each additional = \$10 + \$23 = \$33), the question BEHIND the question asks "Did the office manager spend more than \$33?"

1) The delivery cost for the order totalled more than \$30.00.

If it's \$31, then the answer to the question is NO
If it's \$35, then the answer to the question is YES
Fact 1 is INSUFFICIENT.

2) The average delivery cost of the N chairs was \$1.36.

This information is fantastic because we don't actually have to calculate anything. There's only one value of N that will equal \$1.36 exactly. If you change the N, then the average changes. Fact 2 would be enough to tell us exactly what N is, so we'd be able to answer the question (and there would be JUST ONE answer).
Fact 2 is SUFFICIENT.

Final answer:

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