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# In a stack of boards at a lumber yard, the 20th board

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Senior Manager
Joined: 22 Sep 2005
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In a stack of boards at a lumber yard, the 20th board [#permalink]

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14 Nov 2006, 13:59
4
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18
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Difficulty:

45% (medium)

Question Stats:

53% (00:40) correct 47% (00:42) wrong based on 774 sessions

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In a stack of boards at a lumber yard, the 20th board counting from the top of the stack is immediately below the 16th board counting from the bottom of the stack. How many boards are in the stack?

A. 38
B. 36
C. 35
D. 34
E. 32
[Reveal] Spoiler: OA

Last edited by Bunuel on 03 Sep 2012, 05:12, edited 2 times in total.

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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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03 Sep 2012, 05:18
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vidhya16 wrote:
Guys,

Im confused with the phrase "immediately below 16 from the bottom". When you count something and you say immediately below something doesnt that it mean next number in the counting. In this example it will be 17th. How do you guys say it is 15th from the bottom?

Any clarification will help on Tuesday attempt.

Thanks

In a stack of boards at a lumber yard, the 20th board counting from the top of the stack is immediately below the 16th board counting from the bottom of the stack. How many boards are in the stack?

A. 38
B. 36
C. 35
D. 34
E. 32

There are some number of boards stacked.

20th board from the top is immediately below the 16th board from the bottom:

1
2
3
.
.
.
16
20 15
14
13
.
.
.
3
2
1

As you can see 20th board from the top is immediately below the 16th board from the bottom. The total number of boards 20(red)+14(blue)=34.

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Senior Manager
Joined: 08 Jun 2006
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Location: Washington DC

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14 Nov 2006, 14:32
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20th board from top is 15th (immediately below the 16th board) from bottom. Therefore, there are 14 more boards below the 20th board (from top).
Total number of boards = 34

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Manager
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14 Nov 2006, 14:42
This is where I generally tend to make mistakes, hence I do it the manual way.

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VP
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15 Nov 2006, 06:57
16 th above 20th..

so 20th is 15th..there are 14 under that..total is 34
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Director
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21 Nov 2006, 16:12
1
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Algebraically:
x-19=15
x=34

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Senior Manager
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Re: PS: Stack of boards [#permalink]

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22 Nov 2006, 00:10
In a stack of boards at a lumber yard, the 20th board counting from the top of the stack is immediately below the 16th board counting from the bottom of the stack. how many boards are in the stack?

A) 38

B) 36

C) 35

D) 34

E) 32

123456789 10 11 12 13 14 15 16 17 18 19 20
16 15 14 13 .... 1

18+16=34

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Intern
Joined: 08 Jan 2012
Posts: 7

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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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02 Sep 2012, 08:17
Guys,

Im confused with the phrase "immediately below 16 from the bottom". When you count something and you say immediately below something doesnt that it mean next number in the counting. In this example it will be 17th. How do you guys say it is 15th from the bottom?

Any clarification will help on Tuesday attempt.

Thanks

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Manager
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Concentration: Finance, Economics
Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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04 Sep 2012, 03:52
20th from the top is 15th form the bottom, so there are 14 more boards below the first 20...which is 34 total.
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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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29 Jan 2014, 09:27
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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19 Feb 2015, 09:02
We can actually quickly try it out with lesser number of planks.

Say 4th from the top is immediately below 3rd from the bottom.

-------------
-------------
-------------
-------------
-------------

Total number of planks = 4+3-2 = 5

This in fact would be the case with any plank. For example, 3rd from the top is below 4th from the bottom.

Total number of planks = 3+4-2 = 5

Here, 20th from the top is below 16th from the bottom
-> Total number of planks = 20+16-2 = 34

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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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18 Oct 2015, 12:18
novice12 wrote:
In a Stack of boards at a lumber yard, the 20th board counting from the top of the stack is immediately below the 16th board counting from the bottom of the stack. How many boards are in the stack?
a. 38
b. 36
c. 35
d. 34
e. 32

We need the 20th board, when we start counting from the top.
This board is immediately below the 16th board from the bottom. i.e. This is the 15th board from the bottom
Hence we have 14 more boards below this.

Total number of boards = 14(No. of boards below the one in consideration) + 20(No. of boards above the one in consideration) = 34 Option D
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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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07 Jan 2017, 07:41
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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06 May 2017, 12:42
I'm not entirely sure what this is testing. Is this a pure logic question? Can we expect to see more questions like this on the GMAT and do we have any additional related practice problems?

Thanks!

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Re: In a stack of boards at a lumber yard, the 20th board   [#permalink] 06 May 2017, 12:42
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