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Current Student
Joined: 29 Jan 2005
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1
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4
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Difficulty:

15% (low)

Question Stats:

71% (02:01) correct 29% (00:52) wrong based on 127 sessions

A. 16
B. 32
C. 41
D. 54
E. 68
[Reveal] Spoiler: OA
Director
Joined: 13 Nov 2003
Posts: 793
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The number of beads should fulfill N=5*K+3 .
Seems like E
SVP
Joined: 24 Aug 2006
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Re: PS Series [#permalink]  02 Nov 2006, 06:57
1
KUDOS
GMATT73 wrote:
A necklace is made by stringing N individual beads together in the repeating pattern red, green, white, blue and yellow. If the necklace begins with a red bead and ends with a white bead, then N could equal...

a. 16
b. 32
c. 41
d. 54
e. 68

there are 5 colors that repeat. so total beads=5k(number of repeated beads)+3(red, green, white)

basically, we have to find a number that is 3 more than a multiple of 5.

e.68 is the only number 65+3=68
Manager
Joined: 10 Dec 2007
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1
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BOOKMARKED

A. 16
B. 32
C. 41
D. 54
E. 68

-thanx
CEO
Joined: 17 Nov 2007
Posts: 3578
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
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Kudos [?]: 2132 [1] , given: 359

Re: PS - probability [#permalink]  18 Jan 2008, 10:55
1
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Expert's post
1
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E

20-sec way.

we should find the reminder of n divisible by 5

only 68 has reminder 3.
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Manager
Joined: 10 Dec 2007
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Re: PS - probability [#permalink]  18 Jan 2008, 11:06
walker wrote:
E

20-sec way.

we should find the reminder of n divisible by 5

only 68 has reminder 3.

can u explain me a more simpler way. m not getting your answer.
Director
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Re: PS - probability [#permalink]  18 Jan 2008, 11:35
1
KUDOS
Here's how the necklace looks when it is strung:

RED-GREEN-WHITE-BLUE-YELLOW

We know that the length of the pattern is 5 beads (shown above). The necklace begins at the red bead and then ends in a white bead. The shortest necklace we could have would be RED-GREEN-WHITE, which would only be 3 beads and then fit the bill. The next shortest necklace we could have would be when the pattern of 5 beads has been repeated again. In other words (3+5=8 beads) In this case the pattern would loop once (5 beads), then start RED(6)-GREEN(7)-WHITE(8).

The pattern that emerges here is that the number of beads will be in this list:

3
3+5 = 8
3+5+5 = 13
3+5+5+5 = 18
etc

Any easier way of writing this pattern would be to say that the number of beads must be divisible by 5 with 3 left over. or, when the number is divided by 5 it has a remainder of 3. Then we move onto our choices:

16/5 = 3 remainder 1
32/5 = 6 remainder 2
41/5 = 8 remainder 1
54/5 = 10 remainder 4
68/5 = 13 remainder 3

BINGO! We see that 68 is our answer.

an even shorter method would be to realize that the number must end in 3 or 8 because multiples of 5 end in 0 or 5. Thus, the only choice that ends in 3 or 8 would be our answer!

SVP
Joined: 28 Dec 2005
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Re: PS - probability [#permalink]  18 Jan 2008, 18:14
Recognize that we are going to have to look for an answer thats a multiple of 5, plus 3.

Mutliple of 5 because there are 5 beads in the pattern, and plus 3 because the bead ends on white, which is 3 into the pattern.

I just went through all the answer choices, and only E fits. 5x13 = 65, and 65+3=68
SVP
Joined: 04 May 2006
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Schools: CBS, Kellogg
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Re: PS - probability [#permalink]  18 Jan 2008, 19:26
walker wrote:
E

20-sec way.

we should find the reminder of n divisible by 5

only 68 has reminder 3.

Walker, why it is not multiple of 8? I reason that it is multiple of 8 and I choose A and B, but bewteen A and B I can not decide which one? keke
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Re: PS - probability [#permalink]  18 Jan 2008, 22:16
Expert's post
sondenso wrote:
walker wrote:
E

20-sec way.

we should find the reminder of n divisible by 5

only 68 has reminder 3.

Walker, why it is not multiple of 8? I reason that it is multiple of 8 and I choose A and B, but bewteen A and B I can not decide which one? keke

I cannot write more in 20 sec
Indeed, eschn3am give us a good explanation.
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Manager
Joined: 17 Jul 2010
Posts: 123
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Re: [#permalink]  01 May 2013, 18:06
1
KUDOS
GMATT73 wrote:
There must a simple equation to aplly here, just need a little help setting it up. Counting by brute force is a time waster!

A fast way without heavy calculations is to look at the answers and subtract 3 from the answer, and find if its a multiple of 5. Only option that fits this criteria is E.
Math Expert
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Expert's post
GMATT73 wrote:

A. 16
B. 32
C. 41
D. 54
E. 68

Similar question to practice: 12-easy-pieces-or-not-126366.html#p1033936
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