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Director  Joined: 29 Nov 2012
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A supermarket sells a certain brand of jelly in two jars of different  [#permalink]

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11 00:00

Difficulty:   25% (medium)

Question Stats: 78% (01:50) correct 22% (01:54) wrong based on 269 sessions

### HideShow timer Statistics A supermarket sells a certain brand of jelly in two jars of different sizes, as shown above. Jar A is a right circular cylinder with inside diameter D and inside Height h; Jar B is a right circular cylinder with inside diameter T and inside height 2h. Assuming each jar is filled to capacity, which jar of jelly will cost less per unit volume?

(1) The relationship between the diameters of Jar A and Jar B is 3T = 2D.

(2) Jar A costs $1.59 and Jar B costs 1.39 Attachment: Cylinder.jpg [ 13.67 KiB | Viewed 8976 times ] Originally posted by fozzzy on 18 Jan 2013, 04:49. Last edited by Bunuel on 24 Jan 2019, 04:38, edited 3 times in total. Edited the question. ##### Most Helpful Expert Reply Math Expert V Joined: 02 Sep 2009 Posts: 60480 Re: A supermarket sells a certain brand of jelly in two jars of different [#permalink] ### Show Tags 2 3 A supermarket sells a certain brand of jelly in two jars of different sizes, as shown above. Jar A is a right circular cylinder with inside diameter D and inside Height h; Jar B is a right circular cylinder with inside diameter T and inside height 2h. Assuming each jar is filled to capacity, which jar of jelly will cost less per unit volume? (1) The relationship between the diameters of Jar A and Jar B is 3T = 2D. (2) Jar A costs$1.59 and Jar B costs 1.39

The volume of a cylinder is given by: $$volume_{cylinder}=\pi*{r^2}*h$$.

From (1) we have that t/2=d/3, thus $$volume_A=\pi*{(\frac{d}{2})^2}*h$$ and $$volume_B=\pi*{(\frac{t}{2})^2}*2h=\pi*{(\frac{d}{3})^2}*2h$$.

From (2) we have that 1 unit volume of A costs $$\frac{1.59}{\pi*{(\frac{d}{2})^2}*h}=\frac{4*1.59}{\pi{d^2}h}$$ and 1 unit volume of B costs $$\frac{1.39}{\pi*{(\frac{d}{3})^2}*2h}=\frac{4.5*1.39}{\pi{d^2}h}$$. Now, all we need to do is to see which one is less 4*1.59 or 4.5*1.39.

Hope it's clear.
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Re: A supermarket sells a certain brand of jelly in two jars of different  [#permalink]

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Bunuel wrote: A supermarket sells a certain brand of jelly in two jars of different sizes, as shown above. Jar A is a right circular cylinder with inside diameter D and inside Height h; Jar B is a right circular cylinder with inside diameter T and inside height 2h. Assuming each jar is filled to capacity, which jar of jelly will cost less per unit volume?

(1) The relationship between the diameters of Jar A and Jar B is 3T = 2D.
(2) Jar A costs \$1.59 and Jar B costs 1.39

The volume of a cylinder is given by: $$volume_{cylinder}=\pi*{r^2}*h$$.

From (1) we have that t/2=d/3, thus $$volume_A=\pi*{(\frac{d}{2})^2}*h$$ and $$volume_B=\pi*{(\frac{t}{2})^2}*2h=\pi*{(\frac{d}{3})^2}*2h$$.

From (2) we have that 1 unit volume of A costs $$\frac{1.59}{\pi*{(\frac{d}{2})^2}*h}=\frac{4*1.59}{\pi{d^2}h}$$ and 1 unit volume of B costs $$\frac{1.39}{\pi*{(\frac{d}{3})^2}*2h}=\frac{4.5*1.39}{\pi{d^2}h}$$. Now, all we need to do is to see which one is less 4*1.59 or 4.5*1.39.

Hope it's clear.

Bunuel - Actually my confusion arises with the answer explanation on prep, it says 1.39 / (pi*(2/9D)^2*h) = 6.255 / (pi*D^2*h). I know this is simple algebra but can you walk me through how I could easily convert this in 2 min if I were not able to see that t/2=d/3 and I kept it in the form T=2/3D. Thanks so much for your help with these problems.
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Re: A supermarket sells a certain brand of jelly in two jars of different  [#permalink]

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Hi jmuduke08,

Since this conversation is over a 1.5 years old, I'm not sure if your'e still interested in an explanation, but here goes.

On the GMAT, DS questions sometimes involve "crazy-looking" numbers as a way to test if you can "get around" the crazy numbers and get to the correct answer without doing lots of extensive calculations. In that same way, Problem Solving questions will rarely force you into doing lots of "crazy math" because the GMAT Quant section isn't really a "math test" (by traditional standards). If you CHOOSE to do lots of crazy calculations, then that's on you - most PS questions can be approached in a variety of ways though, so "your way" of doing things might be the "long way."

If the type of prompt that occurs here were to occur in a PS prompt, then you'd likely see the word "approximately" in the wording (so that you wouldn't be forced into doing long-winded and excessive calculations) and you'd have 5 answers to choose from. If the 5 answers were sufficiently "spaced out", then you wouldn't have to do much to solve the problem beyond the basic formulaic set-up, simplification and some estimation/pattern-matching.

Even here, once you combine the two Facts, the two equations have the exact same variables AND are each set equal to a value, so performing the last set of calculations is unnecessary - you KNOW you could figure out which costs less per unit volume, so that is enough to choose the correct answer.

GMAT assassins aren't born, they're made,
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GMAT 2: 620 Q42 V33 Re: A supermarket sells a certain brand of jelly in two jars of different  [#permalink]

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I built up on Bunuel's answers
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Re: A supermarket sells a certain brand of jelly in two jars of different  [#permalink]

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_________________ Re: A supermarket sells a certain brand of jelly in two jars of different   [#permalink] 14 Dec 2019, 11:55
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