The cost of delivery for an order of desk chairs was $10.00 for the fi

Question

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.

Bunuel · Accepted Answer

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.

GyanOne · Answer

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  /n = 1.36 
=> n= 25, which is greater than 24. Sufficient.

The answer is (B).

pele1113 · Answer

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

Thus, B.

kuttingchai · Answer

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

Carcass · Answer

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.

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

Bunuel · Answer

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.

Carcass · Answer

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.

WillEconomistGMAT · Answer

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.

amenon55 · Answer

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

Bunuel · Answer

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.

GMATinsight · Answer

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. 
 /n = 1.36
i.e. 1.36n = 10 + (n-1)
i.e. 0.36n = 9
i.e. n = 25
 SUFFICIENT

Answer: Option B

anupamadw · Answer

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?

Bunuel · Answer

Yes, if it were (9+n)/n>1.36, it still would be sufficient.

MathRevolution · Answer

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

EMPOWERgmatRichC · Answer

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:  B

GMAT assassins aren't born, they're made, 
Rich

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