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M26-15

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Math Expert
Joined: 02 Sep 2009
Posts: 49271

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16 Sep 2014, 01:25
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25% (medium)

Question Stats:

72% (00:49) correct 28% (00:54) wrong based on 196 sessions

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Julie is putting $$M$$ marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of $$M$$?

A. 22
B. 30
C. 38
D. 46
E. 54

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Math Expert
Joined: 02 Sep 2009
Posts: 49271

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16 Sep 2014, 01:25
1
Official Solution:

Julie is putting $$M$$ marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of $$M$$?

A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then $$M=7k+3$$. The only answer choice which is multiple of 7 plus 3 is $$38=35+3$$.

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Manager
Joined: 06 Jun 2013
Posts: 106
Concentration: Technology, General Management
GMAT 1: 680 Q48 V35
GPA: 3.47

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07 Aug 2015, 04:26
Hi Bunuel,

Pls. correct where my understanding is going wrong?

Its given that the marbles are arranged in a row in a repeating pattern starting with Blue, white.....and ending with red marble.

So, we have

blue, white, red, green, black, yellow, pink, blue, white, red (Totally 10 Marbles in each row)

So my question to you if that is the case, then why cannot 30 be the total number of Marbles since it is divisble by 10.

My understanding is that the marbles are arranged in each row as below:

blue, white, red, green, black, yellow, pink, blue, white, red ------------------> Row1 (10 Marbles)
blue, white, red, green, black, yellow, pink, blue, white, red ------------------> Row2 (10 Marbles)
blue, white, red, green, black, yellow, pink, blue, white, red ------------------> Row3 (10 Marbles)

Vijay

Bunuel wrote:
Official Solution:

Julie is putting $$M$$ marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of $$M$$?

A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then $$M=7k+3$$. The only answer choice which is multiple of 7 plus 3 is $$38=35+3$$.

Manager
Joined: 06 Jun 2013
Posts: 106
Concentration: Technology, General Management
GMAT 1: 680 Q48 V35
GPA: 3.47

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07 Aug 2015, 04:33
1
Sorry Bunuel,

I got my mistake. I think I have ignored the word "in a row" in the question.

Realized this only after I posted this query.

Vijay

svijayaug12 wrote:
Hi Bunuel,

Pls. correct where my understanding is going wrong?

Its given that the marbles are arranged in a row in a repeating pattern starting with Blue, white.....and ending with red marble.

So, we have

blue, white, red, green, black, yellow, pink, blue, white, red (Totally 10 Marbles in each row)

So my question to you if that is the case, then why cannot 30 be the total number of Marbles since it is divisble by 10.

My understanding is that the marbles are arranged in each row as below:

blue, white, red, green, black, yellow, pink, blue, white, red ------------------> Row1 (10 Marbles)
blue, white, red, green, black, yellow, pink, blue, white, red ------------------> Row2 (10 Marbles)
blue, white, red, green, black, yellow, pink, blue, white, red ------------------> Row3 (10 Marbles)

Vijay

Bunuel wrote:
Official Solution:

Julie is putting $$M$$ marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of $$M$$?

A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then $$M=7k+3$$. The only answer choice which is multiple of 7 plus 3 is $$38=35+3$$.

Manager
Joined: 03 Oct 2014
Posts: 135
Location: India
Concentration: Operations, Technology
GMAT 1: 720 Q48 V40
WE: Engineering (Aerospace and Defense)

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12 Oct 2015, 23:39
I think this is a high-quality question and the explanation isn't clear enough, please elaborate.
Math Expert
Joined: 02 Sep 2009
Posts: 49271

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13 Oct 2015, 09:51
I think this is a high-quality question and the explanation isn't clear enough, please elaborate.

Can you please be a little bit more specific? Which part is not clear? Thank you.
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Joined: 15 Apr 2015
Posts: 13
Location: India
Schools: EDHEC (A)
GMAT 1: 620 Q44 V31
GPA: 3.25

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16 Oct 2015, 11:25
Bunuel wrote:
I think this is a high-quality question and the explanation isn't clear enough, please elaborate.

Can you please be a little bit more specific? Which part is not clear? Thank you.

couldn't understand the question could you please provide a detailed explanation
Intern
Joined: 28 Dec 2015
Posts: 40

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09 Jun 2016, 01:20
I think this is a high-quality question and the explanation isn't clear enough, please elaborate.

You start placing different color marbles in a row...starting with blue white red green Black yellow pink.and in the same row the last marble has to be red,so you have to again start repeating this pattern until you get the red marble.

{blue white red green Black yellow pink} blue white Red
it would be a multiple of seven + 3 additional tiles=7k+3

From the answer choices,only 38 satisfies this equation.
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Joined: 01 May 2018
Posts: 1

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07 Aug 2018, 22:21
blue, white, red, green, black, yellow, pink.
blue, white, red, green, black, yellow, pink.
blue, white, red, green, black, yellow, pink.
blue (A. 22), white, red, green, black, yellow, pink.
blue, white (B, 30), red, green, black, yellow, pink.
blue, white, red (C 38), green, black, yellow, pink.
blue, white, red, green (D 46), black, yellow, pink.
blue, white, red, green, black (E 54), yellow, pink.
blue, white, red, green, black, yellow, pink.

this makes more sense? i made the mistake of thinking it's B too. but when you lay them out the right answer is C
Intern
Joined: 12 Jan 2017
Posts: 33

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29 Aug 2018, 12:41
Bunuel wrote:
Official Solution:

Julie is putting $$M$$ marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of $$M$$?

A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then $$M=7k+3$$. The only answer choice which is multiple of 7 plus 3 is $$38=35+3$$.

This is a good explanation, but to make it clearer for some:
Consider the string of Blue, White, Red, Green, Black, Yellow and Pink marbles is 7 long. Since the string repeats, you need to divide all of the answers by seven. Then note how the actual string starts and ends. It starts with Blue (position #1), and ends with Red (position #3). Therefore you are looking for an answer that will be a multiple of seven, and have three left over (remainder 3).

To solve, divide all of the answers by 7, and when the remainder is 3 you have an answer.

You can also just count out until you find one that matches.
Re: M26-15 &nbs [#permalink] 29 Aug 2018, 12:41
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