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In a certain appliance store, each model of television is

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In a certain appliance store, each model of television is [#permalink] New post 31 Jul 2012, 12:15
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In a certain appliance store, each model of television is uniquely designated by a code made up of a particular ordered pair of letters. If the store has 60 different models of televisions, what is the minimum number of letters that must be used to make the codes?

A. 6
B. 7
C. 8
D. 9
E. 10


I think the official answer supplied by PR is incorrect.
I Feel that D is the correct answer, they say C.
Am I missing something?
[Reveal] Spoiler: OA

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In a certain appliance store, each model of television is [#permalink] New post 31 Jul 2012, 12:37
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thebogie17 wrote:
In a certain appliance store, each model of television is uniquely designated by a code made up of a particular ordered pair of letters. If the store has 60 different models of televisions, what is the minimum number of letters that must be used to make the codes?

A. 6
B. 7
C. 8
D. 9
E. 10


I think the official answer supplied by PR is incorrect.
I Feel that D is the correct answer, they say C.
Am I missing something?


If n is the number of distinct letters used to create the two lettered codes, then a total of n * n = n^2 different codes can be created. We need n^2\geq60. The smallest n which fulfills this condition is n = 8.

Answer C
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Last edited by EvaJager on 30 Jul 2014, 05:52, edited 2 times in total.
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Re: In a certain appliance store, each model of television is [#permalink] New post 31 Jul 2012, 12:54
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thebogie17 wrote:
In a certain appliance store, each model of television is uniquely designated by a code made up of a particular ordered pair of letters. If the store has 60 different models of televisions, what is the minimum number of letters that must be used to make the codes?

A. 6
B. 7
C. 8
D. 9
E. 10


I think the official answer supplied by PR is incorrect.
I Feel that D is the correct answer, they say C.
Am I missing something?


Notice that we are not told that letters in two-letter code must be different. For example three letters A, B, and C give the following codes:
AA;
BB;
CC;
AB;
BA;
AC;
CA;
BC;
CB.

So, if we have n distinct letters, then we can make n^2 different codes (since each X in XX code can take n values). As there are 60 different models of TV then n^2\geq{60} must hold true. Since n must be an integer then the least value of n is 8.

Answer: C.

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Hope it helps.
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Re: In a certain appliance store, each model of television is [#permalink] New post 20 Dec 2013, 02:36
Bunuel wrote:
Notice that we are not told that letters in two-letter code must be different.

Hey Bunuel,

One doubt regarding this question. Doesn't the phrase "ordered pair" mean nothing in the question? My inference was as it is an ordered pair it should be in alphabetical order.

Please clarify. Thanks.

Last edited by reddevils on 20 Dec 2013, 02:40, edited 1 time in total.
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Re: In a certain appliance store, each model of television is [#permalink] New post 20 Dec 2013, 02:39
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reddevils wrote:
Hey Bunuel,

One doubt regarding this question. Doesn't the phrase "ordered pair" mean nothing in the question? My inference was as it is a ordered pair it should be in alphabetical order.

Please clarify. Thanks.


An ordered pair of letters mean that code AB considered different from code BA, so both are possible.
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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

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Re: In a certain appliance store, each model of television is [#permalink] New post 14 Jan 2014, 21:57
Expert's post
I came up with 2P# + 1C# >= 60
Re: In a certain appliance store, each model of television is   [#permalink] 14 Jan 2014, 21:57
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