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A certain stock exchange designates each stock with a one-, two- or th

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Joined: 30 Mar 2013
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Re: A certain stock exchange designates each stock with a one-, two- or th [#permalink]

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New post 29 Oct 2014, 01:59
I dont know why , but I was thinking for one letter, it's 26,
Then for 2 same ones it would be 26^2
2 different ones would mean 26*25 * 2 (because a different order)
3 same would be 26^3, and 3 different would be 26*25*24*3!....Where am I (obviously) double counting?
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Re: A certain stock exchange designates each stock with a one-, two- or th [#permalink]

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New post 29 Oct 2014, 03:48
usre123 wrote:
I dont know why , but I was thinking for one letter, it's 26,
Then for 2 same ones it would be 26^2
2 different ones would mean 26*25 * 2 (because a different order)
3 same would be 26^3, and 3 different would be 26*25*24*3!....Where am I (obviously) double counting?


How is 26^2 the number of two same letter words? How is 26^3 the number of three same letter words? Isn't both 26? AA, BB, CC, ..., ZZ and AAA, BBB, CCC, DDD, ..., ZZZ?

26^2 gives the number of ALL 2-letter words possible, the same way as 26^3 gives the number of ALL 3-letter words possible.
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Re: A certain stock exchange designates each stock with a one-, two- or th [#permalink]

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New post 30 Nov 2015, 07:35
Hi I have a doubt:

by doing 26^3 are you not counting palindromes? I mean, for example ABA would not be double counted?
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Re: A certain stock exchange designates each stock with a one-, two- or th [#permalink]

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New post 30 Nov 2015, 15:10
lolivaresfer wrote:
Hi I have a doubt:

by doing 26^3 are you not counting palindromes? I mean, for example ABA would not be double counted?


It's fine since the question mentions: "the same letters used in a different order, constitute a different code"
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Re: A certain stock exchange designates each stock with a one-, two- or th [#permalink]

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New post 28 Nov 2017, 20:00
- No. of ways to make one letter code: 26 (we have 26 different letters)
- No. of ways to make 2 letter code: 26 * 26 (each letter can combine with 25 other letter and with itself)
- No. of ways to make 3 letter code: 26 * 26 * 26
=> total possible codes = 26 + 26*26 + 26*26*26 =18278
Hence the answer is E.
Re: A certain stock exchange designates each stock with a one-, two- or th   [#permalink] 28 Nov 2017, 20:00

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