In a certain lab, chemicals are identified by a color-coding : PS Archive
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# In a certain lab, chemicals are identified by a color-coding

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Intern
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In a certain lab, chemicals are identified by a color-coding [#permalink]

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28 Jun 2005, 16:08
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In a certain lab, chemicals are identified by a color-coding system. There are 20 different chemicals. Each one is coded with either a single color or a unique two color pair. If the order of the colors in the pairs doesn't matter, what is the minimum number of different colors needed to code all 20 chemicals with either a single color or a unique pair of colors?

Is it possible to do this problem without knowing the answer choices (w/ the choices, it is simply a matter of putting them into a quick equation)?

I also had another quick question - I have come across the <> symbol quite often in these boards, such as n<>0 etc. What does <> mean?

Thanks.
Director
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28 Jun 2005, 16:30
<> means 'not equal to'

sure you can do it w/o answer choices

just need to solve

n + 0.5*n*(n-1) >= 20
or
n^2 + n - 40 >=0
for a minimum positive integer n
Intern
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28 Jun 2005, 16:37
Could you fully solve your equation.

I dont seem to be getting the right OA after solving the equations you have given.

Thanks.
Director
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28 Jun 2005, 16:40
if n=5, the expression equals -10

if n=6, the expression equals 2 > 0 so 6 is the answer
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28 Jun 2005, 16:42
Got it

Thanks.
Senior Manager
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29 Jun 2005, 06:53
If n is the required number, then it is the smallest positive integer that fulfils the inequality:

C(n,1) + C (n,2) > 19

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29 Jun 2005, 13:12
Thanks ABJ, thats how I arrived at the answer = 6.
6C2 = 15, 6C1 = 6, therefore 6C2 + 6C1 = 21 which is > 19
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