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# White and black blocks are stacked in a vertical column so

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Director
Joined: 15 Aug 2005
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Location: Singapore
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White and black blocks are stacked in a vertical column so [#permalink]  23 Oct 2005, 18:07
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White and black blocks are stacked in a vertical column so that no two blocks of the same color are adjacent. IF there are 247 blocks in the stack, how many white blocks are there in the stack?

A. The top block in the stack is white
B. There are 5 white blocks in the 10 blocks at the bottom of the stack.
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Cheers, Rahul.

Manager
Joined: 14 Apr 2003
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Re: DS-Black/White blocks [#permalink]  23 Oct 2005, 18:12
rahulraao wrote:
White and black blocks are stacked in a vertical column so that no two blocks of the same color are adjacent. IF there are 247 blocks in the stack, how many white blocks are there in the stack?

A. The top block in the stack is white
B. There are 5 white blocks in the 10 blocks at the bottom of the stack.

Is OA A?

1) Would give us the whole stack's combination?
2) This cant tell us what is the lowest block?
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Joined: 05 Apr 2005
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Re: DS-Black/White blocks [#permalink]  23 Oct 2005, 18:16
A. stat i is enough and ii isnot.
VP
Joined: 22 Aug 2005
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A.

as total number of blocks is odd, topmost and bottommost clock is of same color.

(1) total number of White blocks = (int) 247 / 2 + 1 = 124

(2) cannot determine sufficiently the bottommost block
Intern
Joined: 05 May 2005
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We need to find which block is first or last since doing so will tell us which block color has 1 more than the other.

I) sufficient as we know white has the extra block
II) white could be first or black could be first which will give different totals so insufficient

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