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Manager  Joined: 16 Feb 2010
Posts: 154
A right triangle ABC has to be constructed in the xy-plane  [#permalink]

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65 00:00

Difficulty:   55% (hard)

Question Stats: 65% (01:59) correct 35% (02:30) wrong based on 460 sessions

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A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordiantes of A, B and C are to satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. The numbers of different triangles that can be constructed with these properties are?

A. 63
B. 336
C. 567
D. 3024
E. 5040
Math Expert V
Joined: 02 Sep 2009
Posts: 64174

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13
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zisis wrote:
A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordiantes of A, B and C are to satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. The numbers of different triangles that can be constructed with these properties are?

A63
B336
C567
D3024
E5040

Question should specify that x- and y-coordinates of A, B, and C are to be integers.

We have the rectangle with dimensions 9*7 (9 horizontal dots and 7 vertical). AC is parallel to y-axis and AB is parallel to x-axis.

Choose the (x,y) coordinates for vertex A (right angle): 9C1*7C1;
Choose the x coordinate for vertex B (as y coordinate is fixed by A): 8C1, (9-1=8 as 1 horizontal dot is already occupied by A);
Choose the y coordinate for vertex C (as x coordinate is fixed by A): 6C1, (7-1=6 as 1 vertical dot is already occupied by A).

9C1*7C1*8C1*6C1=3024.

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Intern  Joined: 10 Oct 2010
Posts: 19
Location: Texas

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2
zisis wrote:
A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordiantes of A, B and C are to satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. The numbers of different triangles that can be constructed with these properties are?

A63
B336
C567
D3024
E5040

Note: A and C share the same x coordinate. A and B share the same y coordinate.

The x coordinates have 9 options (x = -1,0,1,2,3,4,5,6,7) pick 2: 1 for point B, and 1 for point A and C. 9P2
The y coordinates have 7 options (y= 1,2,3,4,5,6,7) pick 2: 1 for point A and B, and 1 for point C. 7P2
Number of triangles w/ A as the right angle = 9P2 * 7P2 = 3024
Manager  Joined: 08 Sep 2010
Posts: 142
Location: India
WE 1: 6 Year, Telecom(GSM)

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Good question.+1 KUDO
Manager  Joined: 06 Apr 2010
Posts: 99
A right triangle ABC has to be constructed in the xy-plane so that the  [#permalink]

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A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordinates of A, B and C are integers and satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. How many different triangles can be constructed with these properties?

A 63
B 336
C 567
D 3024
E 5040
Current Student Joined: 26 May 2005
Posts: 429
Re: A right triangle ABC has to be constructed in the xy-plane so that the  [#permalink]

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1
udaymathapati wrote:
A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordinates of A, B and C are integers and satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. How many different triangles can be constructed with these properties?
A 63
B 336
C 567
D 3024
E 5040

Its D ,
for point A you can use any of 9 points ( Xaxis) and & 7 points ( y axis points).. hence 63 ways
for B he can use any other 8 points on the X axis
and for C .. any of the other 6 points.
so total 63*8*6 = 3024

Originally posted by sudhir18n on 22 Jun 2011, 02:21.
Last edited by sudhir18n on 22 Jun 2011, 02:22, edited 1 time in total.
Intern  Joined: 11 Sep 2010
Posts: 9
Location: India
GMAT 1: 620 Q49 V25
Re: A right triangle ABC has to be constructed in the xy-plane so that the  [#permalink]

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udaymathapati wrote:
A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordinates of A, B and C are integers and satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. How many different triangles can be constructed with these properties?
A 63
B 336
C 567
D 3024
E 5040

All the cordinates are integer hence,
possible AB values are
{-1,0}, {-1,1} ....{-1,7}: 8 ways
....
{7,-1}, {7,0} ......{7,6}: 8 ways

9*8 ways = 72

for AC values can be
{1,2}, {1,3} .... {1,7} : 6ways
......
{7,1}, {7,2} ..... {7,6} : 6 ways

7*6 = 42

Total = 72 * 42 = 3024 hence D
VP  Joined: 06 Sep 2013
Posts: 1494
Concentration: Finance
Re: A right triangle ABC has to be constructed in the xy-plane  [#permalink]

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2
Units digit has to be 4 to quicken answer choice. 9*7*8*6 = 3024

Hope this helps
Cheers
J
Intern  Joined: 15 Sep 2013
Posts: 32
Concentration: Strategy, Entrepreneurship
GMAT 1: 680 Q47 V36
GMAT 2: 740 Q50 V40
GPA: 3.65
Re: A right triangle ABC has to be constructed in the xy-plane  [#permalink]

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jlgdr wrote:
Units digit has to be 4 to quicken answer choice. 9*7*8*6 = 3024

Hope this helps
Cheers
J

Hi jlgdr... can u plz explain y the units digit has to 4... thanks
Director  Joined: 19 Apr 2013
Posts: 506
Concentration: Strategy, Healthcare
Schools: Sloan '18 (A)
GMAT 1: 730 Q48 V41
GPA: 4
Re: A right triangle ABC has to be constructed in the xy-plane  [#permalink]

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If we look at such questions as three slots that need to be filled with numbers, they become easier.
Intern  Joined: 30 Mar 2013
Posts: 10
Location: India
Re: A right triangle ABC has to be constructed in the xy-plane  [#permalink]

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1
Quote:
A right triangle ABC has to be constructed in the xy-plane so that the right angle is at A and AB is parallel to x axis. The coordiantes of A, B and C are to satisfy the inequalities -1 ≤ x ≤ 7 and 1 ≤ y ≤ 7. The numbers of different triangles that can be constructed with these properties are?

A. 63
B. 336
C. 567
D. 3024
E. 5040

Here we have a rectangle of size 9*7.
There are 9 choices for the x coordinate {-1,0,1,2,3,4,5,6,7}
There are 7 choices for the y coordinate {1,2,3,4,5,6,7}
AB is parallel to the x-axis, so both A & B will have the same y-coordinate. Let us say that is p
AC is parallel to the y-axis, so both A & C will have the same x-coordinate. Let us say that is q
Let us assume the y coordinate of x coordinate of B to be r and the y-coordinate of C be s
So, the coordinates of A are (q,p); B are (r,p); and C are (q,s)

We need to find out overall possible values for p,q,r,s

q and r need to be chosen from the 9 choices for x-coordinate
=> q & r can be chosen in 9*8 = 72 ways

p and s need to be chosen from the 8 choices for y-coordinate
=> p & s can be chosen in 7*6 = 42 ways

Total ways = 72*42 = 3024
Non-Human User Joined: 09 Sep 2013
Posts: 14990
Re: A right triangle ABC has to be constructed in the xy-plane  [#permalink]

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_________________ Re: A right triangle ABC has to be constructed in the xy-plane   [#permalink] 07 Jul 2019, 05:28

# A right triangle ABC has to be constructed in the xy-plane  