Delivery order of desk chairs...Prep 2 Math

[dianapaolasanchez]

The cost of delivery for an order of desk chairs was $10.00 for the first chair, and additional $1.00 for each additional chair in order. If an office manager placed and order for n desk, is n>24?
1) The delivery cost for the order totaled more than $30.00
2) The average (arithmetic mean) delivery cost per chair of the n chairs was $1.36

I think is D, I am not sure, somebody can explain me? Thanks

[jerly_vivek]

IMO B.

I is not sufficient.
22 chairs, less than 24 : total cost $31, greater than 30.
25 chairs, more than 24 : total cost $34, greater than 30

[shrads.jp]

IMO B.

I is not sufficient.
22 chairs, less than 24 : total cost $31, greater than 30.
25 chairs, more than 24 : total cost $34, greater than 30

i want to just correct to wht is written...
It should be 22 chairs,less than 24 : total cost $29.92, less than 30
the other statement is correct
Then the answer can be inferred as B

[mikrodj]

I also think the correct answer choice should be B. Here's how I approached the problem

Total cost = 10 + (n-1)*1 = 9 + n

statement I

total cost > 30 ---> 9 + n > 30 ---> n > 21 well this is insufficient since n could be 22 or 25 cross out A and D

statement II

average = total cost/n = (9 + n)/n = 1.36 since you can calculate the exact value of n this is sufficient to answer the question. If you solve the equation, you get n = 25 sufficient

[RonPurewal]

i want to just correct to wht is written...
It should be 22 chairs,less than 24 : total cost $29.92, less than 30
the other statement is correct
Then the answer can be inferred as B

huh? $29.92?

the price of the order is $10.00 for the first chair, and $1.00 for each additional chair. how did you get these (whole numbers of dollars) to add up to 29 dollars and 92 cents?

[RonPurewal]

I also think the correct answer choice should be B. Here's how I approached the problem

Total cost = 10 + (n-1)*1 = 9 + n

statement I

total cost > 30 ---> 9 + n > 30 ---> n > 21 well this is insufficient since n could be 22 or 25 cross out A and D

statement II

average = total cost/n = (9 + n)/n = 1.36 since you can calculate the exact value of n this is sufficient to answer the question. If you solve the equation, you get n = 25 sufficient

yes.

[pratik.munjal]

Hmm...one of the questions that uses "fixed cost-variable cost principle". One would be very tempted to choose C after a cursory glance. But a detailed approach points to a different thing.

Let the additional chairs be x (I can see people saying, "Uhh...how original!)

From the question, I form an equation

Total Cost = Fixed Cost + Variable Cost

Total Cost = $10 + (x-1) * $1 (Solve this further- $9 + x )

Statement 1-

Total Cost is more than 30.

9+x>30

x>21. So the question is how much more? 1, 2, 22, or 5 billion. In the absence of a "unique solution", reject the answer choice.

Statement 2-

Now we're talking!

9+x/x=1.36

A value for x can be found. Thus statement 2 is sufficient.

The answer is B

[RonPurewal]

One would be very tempted to choose C after a cursory glance. But a detailed approach points to a different thing.

yes indeed. and this is something that you should always keep in mind on data sufficiency -- anything that you are "tempted to pick after a cursory glance" should be regarded with extreme suspicion.

remember that the test is adaptive; if you are scoring high, then you are going to get questions that most people have gotten incorrect. so, put two and two together: if you are looking at a supposedly obvious answer, but most people have missed the problem ... then you know what's going on.

[hitesh.sakkerwal]

The cost of delivery for an order of desk chairs was $10.00 for the first chair, and additional $1.00 for each additional chair in order. If an office manager placed and order for n desk, is n>24?
1) The delivery cost for the order totaled more than $30.00
2) The average (arithmetic mean) delivery cost per chair of the n chairs was $1.36

Doesn't this additional means that it is $1 extra over $10 for n-1 chairs in the order? If that is so then the total cost becomes: 10 + (n-1)11.
This also makes sense as first chair is for $10 and rest of the chairs for $11. and just $1 for additional chairs doesn't make sense.

BUt with my approach the option B does not yield any result. I mean n comes out to be <1. SO I thought the question is not official and may be wrong.

PLease suggest if otherwise.

[RonPurewal]

Doesn't this additional means that it is $1 extra over $10 for n-1 chairs in the order? If that is so then the total cost becomes: 10 + (n-1)11.

no. the way you have this, it's an additional $11 per extra chair.

"an additional $n" means exactly what it says: you add $n to the previous total. there is no trickery here.

This also makes sense as first chair is for $10 and rest of the chairs for $11. and just $1 for additional chairs doesn't make sense.

why not?
read the problem again -- we are talking about a charge for delivery, not the purchase price of the chairs.

in that case, adding $11 for each additional chair would be preposterous.

[hitesh.sakkerwal]

I get that now...thanks.

[RonPurewal]

I get that now...thanks.

sweet

[sachin.w]

Total cost = 10 + (n-1)*1

Could somebody please explain how this is derived?

[jnelson0612]

Total cost = 10 + (n-1)*1

Could somebody please explain how this is derived?

Sure. Let's say that we buy 5 chairs. That is going to cost $14. I have to pay $10 for the first chair and then $1 for each of the four additional chairs. If n=5, then $10 + (5-1) * $1.

Thus, I am taking $10 (first chair) + (n-1)[which is the number of remaining chairs in the order once I subtract out the first chair, since n is the total number of chairs] * $1 for each of those remaining chairs.

Make more sense?

[sachin.w]

It does make sense now .

Thanks Jamie :).