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# ABC is a right angle triangle, which is 90 degree at A.

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Math Expert
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ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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Updated on: 30 Nov 2017, 05:41
00:00

Difficulty:

45% (medium)

Question Stats:

67% (01:44) correct 33% (01:42) wrong based on 143 sessions

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ABC is a right angle triangle, which is 90 degree at A. What is the Area of the triangle ABC?

1) AB + AC = 8.
2) The largest side is 5$$\sqrt{2}$$.

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html

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Originally posted by chetan2u on 23 Jan 2016, 21:48.
Last edited by chetan2u on 30 Nov 2017, 05:41, edited 2 times in total.
..
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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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24 Jan 2016, 07:59
Triangle is right angled at A. So BC is the hypotenuse.
Area = 1/2*(AB)*(AC)

St1: AB + AC = 8 --> Not sufficient as we get multiple possibilities for AB and AC

St2: BC = 5*sqrt(2) --> Not sufficient to determine the area

Combining St1 and St2,
AB^2 + AC^2 = BC^2......(1)
AB + AC = 8 and BC = 5*sqrt(2)
Only AB = 7, AC = 1 or AC = 7, AB = 1 satisfies (1). Thus AB*AC = 7. Area can be found out
St1 and St2 together is sufficient

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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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24 Jan 2016, 10:51
ABC is a right angle triangle, which is 90 degree at A. What is the Area of the triangle ABC?
1) AB + AC = 8.
2) The largest side is 52√.

AB^2 + AC^2 = BC^2......(1)
AB + AC = 8 and BC = 5*sqrt(2)
Only AB = 7, AC = 1 or AC = 7, AB = 1 satisfies (1). Thus AB*AC = 7. Area can be found out
St1 and St2 together is sufficient

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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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26 Jan 2016, 21:37
1
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

ABC is a right angle triangle, which is 90 degree at A. What is the Area of the triangle ABC?

1) AB + AC = 8.
2) The largest side is 5 √ 2

When you modify the original condition and the question, for the right angle triangle, there are 2 variables(the base line and height), which should match with the number of equations. So you need 2 equations. For 1) 1equation, for 2) 1 equation, which is likely to make C the answer.
When 1) & 2), they become AB^2+AC^2=(5√2)^2=50, (AB+AC)^2=8^2=64, AB^2+AC^2+2AB*AC=64 → 50+2AB*AC=64, AB*AC/2=7/2, which is unique and sufficient.

--> For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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27 Jan 2016, 03:02
ABC is a right angle triangle, which is 90 degree at A. What is the Area of the triangle ABC?
1) AB + AC = 8.
2) The largest side is 52√.

AB^2 + AC^2 = BC^2......(1)
AB + AC = 8 and BC = 5*sqrt(2)
Only AB = 7, AC = 1 or AC = 7, AB = 1 satisfies (1). Thus AB*AC = 7. Area can be found out
St1 and St2 together is sufficient

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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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28 Apr 2016, 07:16
Vyshak wrote:
Triangle is right angled at A. So BC is the hypotenuse.
Area = 1/2*(AB)*(AC)

St1: AB + AC = 8 --> Not sufficient as we get multiple possibilities for AB and AC

St2: BC = 5*sqrt(2) --> Not sufficient to determine the area

Combining St1 and St2,
AB^2 + AC^2 = BC^2......(1)
AB + AC = 8 and BC = 5*sqrt(2)
Only AB = 7, AC = 1 or AC = 7, AB = 1 satisfies (1). Thus AB*AC = 7. Area can be found out
St1 and St2 together is sufficient

Understood...But when similar question with different Question is given....I have to try with the different no's and if i get two pairs solving the equation, then i should choose 'E'.

Pls correct if my understanding is wrong.

Thanks,
A
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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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28 Apr 2016, 07:26
ArunpriyanJ wrote:

Understood...But when similar question with different Question is given....I have to try with the different no's and if i get two pairs solving the equation, then i should choose 'E'.

Pls correct if my understanding is wrong.

Thanks,
A

If there is another question that asks you the area of triangle ABC without telling you which one is the right angle, then yes, there is a high probability that E will be the answer. You have to take it on a case by case basis.

Hope this helps.
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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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30 Nov 2017, 05:25
Why isn't the answer B? If the longest side (hypotenuse) is 5sq.rt.2, then wouldn't that make the other 2 sides 5 and 5?
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Re: ABC is a right angle triangle, which is 90 degree at A.  [#permalink]

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30 Nov 2017, 05:32
meganbailey wrote:
Why isn't the answer B? If the longest side (hypotenuse) is 5sq.rt.2, then wouldn't that make the other 2 sides 5 and 5?

hi

there will be numerous ways /triangles where hypotenuse is $$5\sqrt{2}$$..
$$a^2+b^2=(5\sqrt{2})^2......a^2+b^2=50$$
say a is 7, b will be 1
a is 6, b will be $$\sqrt{50-36}=\sqrt{24}=2\sqrt{6}$$

hope it helps
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html

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Re: ABC is a right angle triangle, which is 90 degree at A.   [#permalink] 30 Nov 2017, 05:32
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