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If Line A and Line B are parallel to each other and 7 points are

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Director
Joined: 18 Feb 2019
Posts: 520
Location: India
GMAT 1: 460 Q42 V13
GPA: 3.6
If Line A and Line B are parallel to each other and 7 points are  [#permalink]

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07 May 2019, 09:46
12
00:00

Difficulty:

45% (medium)

Question Stats:

62% (01:53) correct 38% (01:55) wrong based on 89 sessions

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If Line A and Line B are parallel to each other and 7 points are marked on Line A and 9 points are marked on Line B, how many triangles can be formed whose vertices are among those marked points?

A. 63
B. 189
C. 252
D. 324
E. 441
Director
Joined: 19 Oct 2018
Posts: 697
Location: India
Re: If Line A and Line B are parallel to each other and 7 points are  [#permalink]

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07 May 2019, 11:48
1
2
Total number of triangles possible
= (7C1 * 9C2) + (7C2 * 9C1)
= 252+189
=441
Intern
Joined: 27 Apr 2019
Posts: 4
Re: If Line A and Line B are parallel to each other and 7 points are  [#permalink]

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19 Jun 2019, 22:04
Could someone explain this?
Intern
Joined: 15 Jun 2015
Posts: 2
Re: If Line A and Line B are parallel to each other and 7 points are  [#permalink]

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21 Jun 2019, 03:33
Williamhomey12 wrote:
Could someone explain this?

We can create a triangle by choosing 2 points from line A and 1 point from line B or choosing 2 points from line B and 1 point from line A.
Option 1: 2 points from A and 1 point from B: We have 7C2 ways choosing 2 points from A (dont care about orders so we use C) and 9 ways choosing 1 points from B) -> 7C2*9
Option 2: 9C2*7
-> Total = 7C2*9 + 9C2*7 = 441
Re: If Line A and Line B are parallel to each other and 7 points are   [#permalink] 21 Jun 2019, 03:33
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