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Re: Permutations 1 [#permalink]
23 Aug 2009, 20:09
rohansherry wrote:
IMO B. 8c3 - 1
A is the general stmt. we know that Triangle is fromed using only 3 points.
Agree with B. But I think the combination formula might be wrong.
IMHO, only 3 points are collinear, all the other 5 points are not on the same line. Hence, each of the 3 points can be combined with 2 of the 5 points to create a triangle.
Therefore, the # of triangles = 3 x 5C2 = 3 x 10 = 30.
Last edited by Jivana on 23 Aug 2009, 20:22, edited 1 time in total.
Re: Permutations 1 [#permalink]
23 Aug 2009, 20:20
Jivana wrote:
rohansherry wrote:
IMO B. 8c3 - 1
A is the general stmt. we know that Triangle is fromed using only 3 points.
Agree with B. But I think the combination formula might be wrong.
IMHO, only 3 points are collinear, all the other 5 points are not on the same line. Hence, each of the 3 points can be combined with 2 of the 5 points to create a triangle.
Therefore, the # of triangles = 3 x 5C3 = 3 x 10 = 30.
You forgot 2 of the 3 points (collinear) and 1 of the 5 points to form a triangle. _________________
Re: Permutations 1 [#permalink]
25 Aug 2009, 05:35
HI Guys, My answer would also be B. But, I am not clear in the possibilities to form triangles. 1. using the 3 non collinear : 5C3 2. using one collinear and 2 non collinear : 3C1x5C2
I am sure that I am missing something here. Would you please be of any help to understand the 55 possibilities?
Re: Permutations 1 [#permalink]
26 Aug 2009, 04:27
Guys, I am sorry that it took me so long to post the OA. But here it is:
1. is insufficient because it just states a well known fact 2. is sufficient because in such case we can calculate the number of triangles that can be formed: 5C3+8*3C2+3C1*5C2
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