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A researcher plans to identify each participant in a certain medical

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Re: A researcher plans to identify each participant in a certain medical  [#permalink]

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New post 06 Nov 2018, 09:11
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Re: A researcher plans to identify each participant in a certain medical  [#permalink]

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New post 28 Jan 2019, 07:50
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Got tripped up a bit on the wording, but saw the familiarity of the problem. The hard part is that these combination/permutation word problems express things in an particular way that doesn't always make it immediately clear whether order matters or not.

The issue I had was with the use of the word order, which in my mind would typically be associated with permutations, but the restriction of the problem actually means it's a combination.

"written in alphabetical order" - meaning that the letters have to be alphabetically ordered, but not necessarily consecutively next to each other on the alphabet. This actually makes it a combination and not a permutation question, because it removes all the other possibilities (i.e. we can have AB but not BA). Drawing it out makes sense:

Image

The fact that the letters have to be ordered alphabetically is a convoluted way of saying only unique combinations of letters matter. Hopefully my thinking is correct in this regard.
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Re: A researcher plans to identify each participant in a certain medical  [#permalink]

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New post 28 Jan 2019, 19:17
sarb wrote:
A researcher plans to identify each participant in a certain medical experiment with a code consisting of either a single letter or a pair of distinct letters written in alphabetical order. What is the least number of letters that can be used if there are 12 participants, and each participant is to receive a different code?

A. 4
B. 5
C. 6
D. 7
E. 8


Constraints:
"Single Letter or a pair of distinct letters written in alphabetical order"

List the possibilities out:
A, AB, B, AC, BC, C, AD, BD, CD, D, AE, BE <= 12th combo

A, B, C, D, E were used, 5 different letters.

Answer is B
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Re: A researcher plans to identify each participant in a certain medical  [#permalink]

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New post 04 Feb 2019, 22:49
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How do we choose between C2n and P2n?
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Re: A researcher plans to identify each participant in a certain medical   [#permalink] 04 Feb 2019, 22:49

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