Jul 19 08:00 AM PDT  09:00 AM PDT The Competition Continues  Game of Timers is a teambased competition based on solving GMAT questions to win epic prizes! Starting July 1st, compete to win prep materials while studying for GMAT! Registration is Open! Ends July 26th Jul 20 07:00 AM PDT  09:00 AM PDT Attend this webinar and master GMAT SC in 10 days by learning how meaning and logic can help you tackle 700+ level SC questions with ease. Jul 21 07:00 AM PDT  09:00 AM PDT Attend this webinar to learn a structured approach to solve 700+ Number Properties question in less than 2 minutes
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 56269

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
06 Nov 2018, 10:11
sacmenon wrote: BunuelA,B,AD,C,BC, ABC,D,CD, ABCD,AD,AC,BD so effectively we have used 4 letters. Please read the question carefully: a code consists of either a single letter or a pair of distinct letters written in alphabetical order.
_________________



Senior Manager
Status: Gathering chakra
Joined: 05 Feb 2018
Posts: 365

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
28 Jan 2019, 08:50
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: 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.



Intern
Joined: 19 Jan 2018
Posts: 49

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
28 Jan 2019, 20:17
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



Manager
Joined: 21 Jul 2018
Posts: 193

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
02 Apr 2019, 08:13
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 Bunuel, chetan2uCan any one elaborate condition of highlighted part.
_________________
______________________________ Press +1 Kudos if my post helped you a little and help me to ulcock the tests Wish you all success I'd appreciate learning about the grammatical errors in my posts
Please let me know if I'm wrong somewhere and help me to learn



CEO
Joined: 12 Sep 2015
Posts: 3847
Location: Canada

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
02 Apr 2019, 09:05
Gmatprep550 wrote: 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 Bunuel, chetan2uCan any one elaborate condition of highlighted part. It means that the letters we choose must be presented in alphabetical order. So, for example, EG is good, since E comes before G in the alphabet. Conversely, GE is not acceptable, since G does not come before E in the alphabet. Cheers, Brent
_________________
Test confidently with gmatprepnow.com



Intern
Joined: 23 Dec 2017
Posts: 2

A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
20 Apr 2019, 19:47
A simpler way would be to see the first option, which says 4. If we take 4 alphabets then the number of words with one alphabet : 4 two alphabets(considering 4 & sequence) : 3 two alphabets(considering 3 & sequence) : 2 two alphabets(considering 2 & sequence) :1 Total =10 Hence the next higher to 4 ie 5 is the correct option



Intern
Joined: 04 Feb 2014
Posts: 1

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
29 May 2019, 01:02
Bunuel, can you explain why this is a combination and not a permutation? Bunuel wrote: Almost identical question:
John has 12 clients and he wants to use color coding to identify each client. If either a single color or a pair of two different colors can represent a client code, what is the minimum number of colors needed for the coding? Assume that changing the color order within a pair does not produce different codes. A. 24 B. 12 C. 7 D. 6 E. 5
The concept is not that hard. We can use combination or trial and error approach.
Combination approach: Let # of colors needed be \(n\), then it must be true that \(n+C^2_n\geq{12}\) (\(C^2_n\)  # of ways to choose the pair of different colors from \(n\) colors when order doesn't matter) > \(n+\frac{n(n1)}{2}\geq{12}\) > \(2n+n(n1)\geq{24}\) > \(n(n+1)\geq{24}\) > as \(n\) is an integer (it represents # of colors) \(n\geq{5}\) > \(n_{min}=5\).
Trial and error approach: If the minimum number of colors needed is 4 then there are 4 single color codes possible PLUS \(C^2_4=6\) twocolor codes > 4+6=10<12 > not enough for 12 codes;
If the minimum number of colors needed is 5 then there are 5 single color codes possible PLUS \(C^2_5=10\) twocolor codes > 5+10=15>12 > more than enough for 12 codes.
Actually as the least answer choice is 5 then if you tried it first you'd get the correct answer right away.
Answer: E.
Hope it helps.



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 14563
Location: United States (CA)

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
29 May 2019, 19:32
Hi crushorange, The last sentence in the prompt tells us: "Assume that changing the color order within a pair does NOT produce different codes." This means that two different colors will only produce ONE code. For example BlueGreen and GreenBlue are the SAME code. Thus, the order of the colors does NOT matter and we're dealing with a Combination. GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/



Intern
Joined: 28 Nov 2016
Posts: 1

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
12 Jul 2019, 10:20
A,B,AB,C,AC,BC,D,AD,BD,CD,E,AE....
5 Letters and we can get 12 code in alphabetical order.
Is it the right way of doing it?



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 14563
Location: United States (CA)

Re: A researcher plans to identify each participant in a certain medical
[#permalink]
Show Tags
12 Jul 2019, 11:43
Hi sk710, Based on the work that you've shown, you used a 'brute force' approach (re: you just 'mapped out' the possibilities without the need of a formula or any excessive 'math'). That's actually a great way to approach this question  and you'll find that a certain number of Quant questions (including many DS questions) can be solved by taking that same general approach. GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/




Re: A researcher plans to identify each participant in a certain medical
[#permalink]
12 Jul 2019, 11:43



Go to page
Previous
1 2 3 4
[ 70 posts ]



