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Is quadrilateral ABCD a rectangle?

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Is quadrilateral ABCD a rectangle? [#permalink] New post 09 Sep 2010, 06:42
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Is quadrilateral ABCD a rectangle?

(1) Angle ABC = 90 degrees
(2) AB = CD
[Reveal] Spoiler: OA
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Re: Rectangles [#permalink] New post 09 Sep 2010, 06:59
agnok wrote:
Is quadrilateral ABCD a rectangle?

1. angle ABC = 90 degrees
2. AB=CD

Please explain your solution.


E

1. ABC = 90 ................ other angles can be of any value.

2. AB = CD ............... AC and BD might not be equal.

For rectangle, all angles have to be equal (hence, 90) and opposite sides should be equal. Neither of the two statement helps in determining if the two requirements are satisfied or not.
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Re: Rectangles [#permalink] New post 09 Sep 2010, 07:08
E

for rectangle = all have to be 90 and opp sides equal
1. ABC= 90 : dont know about other angles - insuff
2. AB= CD , other sides may or may not be equal - insuff

together - not necessarily a rectangle, may be a square - insuff
Ans is E
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Re: Rectangles [#permalink] New post 09 Sep 2010, 07:18
E

It may be a square.
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Re: Rectangles [#permalink] New post 09 Sep 2010, 08:02
Expert's post
agnok wrote:
Is quadrilateral ABCD a rectangle?

1. angle ABC = 90 degrees
2. AB=CD

Please explain your solution.


A rectangle is a quadrilateral with four right angles - this is necessary and sufficient condition for quadrilateral to be a rectangle.

(1) angle ABC = 90 degrees --> we know nothing about other angles. Not sufficient.
(2) AB=CD --> opposite sides AB and CD are equal, clearly insufficient.

(1)+(2) Look at the diagram:
Attachment:
rectangle.PNG
rectangle.PNG [ 4.39 KiB | Viewed 1738 times ]
It's possible quadrilateral to be a rectangle (case ABCD1) and it's also possible quadrilateral not to be a rectangle (case ABCD2). Not sufficient.

saxenashobhit wrote:
E

for rectangle = all have to be 90 and opp sides equal
1. ABC= 90 : dont know about other angles - insuff
2. AB= CD , other sides may or may not be equal - insuff

together - not necessarily a rectangle, may be a square - insuff
Ans is E

metallicafan wrote:
E

It may be a square.


It's not necessary ABCD to be square (look at the diagram, it can be simple rectangle). In fact if we knew that ABCD is a square then statements would be sufficient, because square is a special type of rectangle, which means that every square is a rectangle (but not vise-versa).

Hope it helps.
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Re: Rectangles [#permalink] New post 09 Sep 2010, 11:07
The diagram made the difference in understanding the answer.. thanks
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Re: Rectangles [#permalink] New post 12 Sep 2010, 08:59
Thanks Bunuel for the diagram
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Re: Rectangles [#permalink] New post 18 Apr 2014, 03:02
Bunuel wrote:
agnok wrote:
Is quadrilateral ABCD a rectangle?

1. angle ABC = 90 degrees
2. AB=CD

Please explain your solution.


A rectangle is a quadrilateral with four right angles - this is necessary and sufficient condition for quadrilateral to be a rectangle.

(1) angle ABC = 90 degrees --> we know nothing about other angles. Not sufficient.
(2) AB=CD --> opposite sides AB and CD are equal, clearly insufficient.

(1)+(2) Look at the diagram:
Attachment:
rectangle.PNG
It's possible quadrilateral to be a rectangle (case ABCD1) and it's also possible quadrilateral not to be a rectangle (case ABCD2). Not sufficient.

saxenashobhit wrote:
E

for rectangle = all have to be 90 and opp sides equal
1. ABC= 90 : dont know about other angles - insuff
2. AB= CD , other sides may or may not be equal - insuff

together - not necessarily a rectangle, may be a square - insuff
Ans is E

metallicafan wrote:
E

It may be a square.


It's not necessary ABCD to be square (look at the diagram, it can be simple rectangle). In fact if we knew that ABCD is a square then statements would be sufficient, because square is a special type of rectangle, which means that every square is a rectangle (but not vise-versa).

Hope it helps.


HI Bunnel,

One doubt. Here it is mentioned that angle ABC are 90 degrees. and quadrilateral have total of 360 degree. so fourth one should be 90 degree.

then why you have mentioned following statement.

angle ABC = 90 degrees --> we know nothing about other angles. Not sufficient

Thanks
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Re: Rectangles [#permalink] New post 18 Apr 2014, 03:32
Expert's post
PathFinder007 wrote:
Bunuel wrote:
agnok wrote:
Is quadrilateral ABCD a rectangle?

1. angle ABC = 90 degrees
2. AB=CD

Please explain your solution.


A rectangle is a quadrilateral with four right angles - this is necessary and sufficient condition for quadrilateral to be a rectangle.

(1) angle ABC = 90 degrees --> we know nothing about other angles. Not sufficient.
(2) AB=CD --> opposite sides AB and CD are equal, clearly insufficient.

(1)+(2) Look at the diagram:
Attachment:
rectangle.PNG
It's possible quadrilateral to be a rectangle (case ABCD1) and it's also possible quadrilateral not to be a rectangle (case ABCD2). Not sufficient.

saxenashobhit wrote:
E

for rectangle = all have to be 90 and opp sides equal
1. ABC= 90 : dont know about other angles - insuff
2. AB= CD , other sides may or may not be equal - insuff

together - not necessarily a rectangle, may be a square - insuff
Ans is E

metallicafan wrote:
E

It may be a square.


It's not necessary ABCD to be square (look at the diagram, it can be simple rectangle). In fact if we knew that ABCD is a square then statements would be sufficient, because square is a special type of rectangle, which means that every square is a rectangle (but not vise-versa).

Hope it helps.


HI Bunnel,

One doubt. Here it is mentioned that angle ABC are 90 degrees. and quadrilateral have total of 360 degree. so fourth one should be 90 degree.

then why you have mentioned following statement.

angle ABC = 90 degrees --> we know nothing about other angles. Not sufficient

Thanks


Yes, the Sum of Interior Angles of a polygon is 180(n-2) degrees, where n is the number of sides (so is the number of angles). Thus the sum of the interior angles of a quadrilateral is 180*2=360 degrees.

But knowing that one of the angles of a quadrilateral is 90 degrees does not mean that the other angles must also be 90 degrees. The sum of the remaining three angles must be 360-90=270 degrees. So, the remaining three angles can be 100, 100 and 70 or 100, 110, and 60, ...

Hope it's clear.

Hope it's clear.
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Re: Is quadrilateral ABCD a rectangle? [#permalink] New post 10 May 2014, 11:00
Q1.
statement1>parallelogram
statement2>rectangle only if statement1 is true
answer:"C"
Q2.
answer:"B"
Q3
statement1>rectangle meaning all angles are 90
statement2> rhombus...
together it becomes a square..answer:"C"
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Re: Is quadrilateral ABCD a rectangle? [#permalink] New post 11 May 2014, 05:04
Expert's post
ravishankar1788 wrote:
Q1.
statement1>parallelogram
statement2>rectangle only if statement1 is true
answer:"C"
Q2.
answer:"B"
Q3
statement1>rectangle meaning all angles are 90
statement2> rhombus...
together it becomes a square..answer:"C"


Please note that the OA is E, not C. Check here: is-quadrilateral-abcd-a-rectangle-100729.html#p778263

Hope it helps.
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NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: Is quadrilateral ABCD a rectangle?   [#permalink] 11 May 2014, 05:04
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