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

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

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New post 14 Nov 2006, 12:59
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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, 04:12, edited 2 times in total.
OA added.
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New post 14 Nov 2006, 13:32
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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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New post 14 Nov 2006, 13:42
This is where I generally tend to make mistakes, hence I do it the manual way.
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New post 15 Nov 2006, 05:57
16 th above 20th..

so 20th is 15th..there are 14 under that..total is 34 :-D
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Algebraically:
x-19=15
x=34
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Re: PS: Stack of boards [#permalink]

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New post 21 Nov 2006, 23:10
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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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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New post 02 Sep 2012, 07:17
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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Re: In a stack of boards at a lumber yard, the 20th board [#permalink]

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New post 03 Sep 2012, 04:18
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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.

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

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New post 04 Sep 2012, 02:52
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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New post 19 Feb 2015, 08:02
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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New post 18 Oct 2015, 11:18
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

Please support your answer with explanation.


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

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New post 13 Jan 2018, 09:09
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netcaesar 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


Let's start from the bottom and work our way up:

We'll start with the 16th board counting from the bottom of the stack

Right BELOW that 16th board, we have a board that we'll call Larry.
So, Larry is the 15th board counting from the bottom of the stack.
So, starting from the bottom and working our way up to Larry, we have 15 boards so far.

Larry is the 20th board counting from the TOP of the stack
In other words, there are 19 boards ABOVE Larry.
So, including those 19 boards, we now have 34 boards in TOTAL.

Answer: D

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Brent
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Re: In a stack of boards at a lumber yard, the 20th board   [#permalink] 13 Jan 2018, 09:09
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