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# A store currently charges the same price for each towel that

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Re: PS numbers [#permalink]

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08 May 2011, 19:36
let price for each towel = x

then 120/x = number of towels purchased.

(120/x) -10 = (120/(x+1)

substituting x = 3, LHS = RHS = 30 .

Hence C.
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Re: PS numbers [#permalink]

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11 May 2011, 04:09
n*p = (n - 10)(p+1)

np = 120

120 = (120/p - 10) (p+1)

120p = (120 - 10p)(p+1)

12p = (12-p)(p+1)

Checking the values, p = 3

Answer - C
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Re: 600-700 level question [#permalink]

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04 Oct 2011, 20:29
To solve algebraically, set up two equations and then set them equal to one another.

p = price of towel
t = number of towels

Equation 1) pt = 120 => p = 120/t
Equation 2) (p + 1) * (t - 10) = 120

pt = (p + 1) * (t - 10)
pt = pt - 10p + t - 10
10 = -10p + t
10 = -10 * (120 / t) + t
10t = -1200 + t^2
t^2 - 10t - 1200 = 0
(t + 30) * (t - 40) = 0
t = - 30 or t = 40

Since t is the number of towels, it can only be a positive number, and thus t = 40. Since you want the current price of each towel, or p, divide 120 by 40 (equation 1) to get p = 3.

Alternatively, you can also plug in the answer choices to avoid algebra.

pt = 120

A) p = 1; t = 120
B) p = 2; t = 60
C) p = 3; t = 40
D) p = 4; t = 30
E) p = 12; t = 10

Just from that, you can tell that by increasing the price by $1 from$3 to $4, 10 fewer towels can be bought for$120. Thus the answer is C.
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Re: 600-700 level question [#permalink]

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04 Oct 2011, 23:41
Good solutions sesamemochi, but I'd like to modify it slightly to make it faster to solve. From my experience, I would say that we must always try to form an equation in the variable that we need to calculate. This will save us one step at the end. For example, I would solve this problem as below -

Assume the current price to be x. So, as per the given information, we can form the below equation -
120/x = 120/(x+1) + 10

Solving this equation for x, we get 3 and -4
Choose 3 as price cannot be negative.

Secondly, for your alternate 'value plugging' approach, time can be saved if only the options with consecutive prices are considered. In this case 1, 2, 3, 4. But since 12 is not in the sequence, there was no need to even consider option E.

Lastly, in most cases, I find plugging of values a risky affair. Even plugging requires thinking, for example in this case even after plugging the values, only the results of consecutive price pairs matter, such as 1,2 ; 2,3 and 3,4. And imagine if option D was 5 instead of 4, then the plugging would have been useless. Moreover if someone does all the plugging and calculations and later realizes that there are no consecutive pairs to consider, it will be such a waste of time.
My 2 cents - All in all, I suggest that we use value plugging as the last resort. It is more important to know the concepts. Value plugging needs thinking too, so better apply thoughts to applying the concepts.
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p!yu$h http://gmatclub.com/forum/from-620-to-710-my-gmat-story-test-date-30-oct-122547.html#p995276 Manager Joined: 16 Feb 2012 Posts: 237 Concentration: Finance, Economics Followers: 7 Kudos [?]: 294 [0], given: 121 Re: A store currently charges the same price for each towel that [#permalink] ### Show Tags 24 Mar 2012, 13:51 I don't understand how do you come from pxq =120 to (p+1) x (q-10) = 120 Please explain! Thanks! _________________ Kudos if you like the post! Failing to plan is planning to fail. Math Expert Joined: 02 Sep 2009 Posts: 37114 Followers: 7255 Kudos [?]: 96633 [0], given: 10770 Re: A store currently charges the same price for each towel that [#permalink] ### Show Tags 24 Mar 2012, 14:00 Stiv wrote: I don't understand how do you come from pxq =120 to (p+1) x (q-10) = 120 Please explain! Thanks! Let the current price be $$p$$ and the # of towels sold at this price be $$n$$. Then we would have two equations: "If the current price of each towel were to be increased by$1, 10 fewer of the towels could be bought for $120": $$pn=120$$ amd $$(p+1)(n-10)=120$$, so the same$120 can buy $$n$$ towels for $$p$$ each or $$n-1$$ towels for $$(p+1)$$ each.

For complete solution check this: a-store-currently-charges-the-same-price-for-each-towel-that-30571-20.html#p782872

Hope it helps.
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15 Sep 2013, 18:35
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Re: A store currently charges the same price for each towel that [#permalink]

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20 Nov 2013, 17:02
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chiragr wrote:
A store currently charges the same price for each towel that it sells. If the current price of each towel were to be increased by $1, 10 fewer of the towels could be bought for$120, excluding sales tax. What is the current price of each towel?

A) 1
B) 2
C) 3
D) 4
E) 12

WoW! It was a lot of Maths up there!

A simple approach can be the use of answer choices:

A) If current price is 1$, then we get 120 Towels, but if price is increase by 1$ to 2, then we get 60 Towels.............. Difference Not 10$B) If current price is 2$, then we get 60 Towels, but if price is increase by 1$to 3, then we get 40 Towels................ Difference Not 10$
C) If current price is 3$, then we get 40 Towels, but if price is increase by 1$ to 4, then we get 30 Towels................ Difference is 10$Current Student Joined: 06 Sep 2013 Posts: 2035 Concentration: Finance GMAT 1: 770 Q0 V Followers: 64 Kudos [?]: 605 [1] , given: 355 Re: A store currently charges the same price for each towel that [#permalink] ### Show Tags 26 Dec 2013, 07:09 1 This post received KUDOS chiragr wrote: A store currently charges the same price for each towel that it sells. If the current price of each towel were to be increased by$1, 10 fewer of the towels could be bought for $120, excluding sales tax. What is the current price of each towel? A) 1 B) 2 C) 3 D) 4 E) 12 These questions are perfect for backsolving instead of solving quadratics Always start with C and gauge whether you need more or less, answer choices are normally arranged from lowest to highest Hope it helps Oh and BTW yeah answer is C Kudos Rain!! Cheers! J:) Manager Joined: 21 Aug 2013 Posts: 113 Schools: ISB '15 Followers: 2 Kudos [?]: 30 [0], given: 60 Re: A store currently charges the same price for each towel that [#permalink] ### Show Tags 01 Mar 2014, 03:54 Hi, I know this is a OG question. Still from the below text how can we assume that the current P X Q = 120. A store currently charges the same price for each towel that it sells. If the current price of each towel were to be increased by$1, 10 fewer of the towels could be bought for $120, excluding sales tax. What is the current price of each towel? _________________ Veritas Prep - 650 MGMAT 1 590 MGMAT 2 640 (V48/Q31) Please help the community by giving Kudos. Math Expert Joined: 02 Sep 2009 Posts: 37114 Followers: 7255 Kudos [?]: 96633 [0], given: 10770 Re: A store currently charges the same price for each towel that [#permalink] ### Show Tags 01 Mar 2014, 05:49 seabhi wrote: Hi, I know this is a OG question. Still from the below text how can we assume that the current P X Q = 120. A store currently charges the same price for each towel that it sells. If the current price of each towel were to be increased by$1, 10 fewer of the towels could be bought for $120, excluding sales tax. What is the current price of each towel? The price increase and quantity decrease are linked with the amount of$120, how else?

OPEN DISCUSSION OF THIS QUESTION IS HERE: a-store-currently-charges-the-same-price-for-each-towel-that-144780.html
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Re: A store currently charges the same price for each towel that   [#permalink] 01 Mar 2014, 05:49

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