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by Sunny22uk » Fri Sep 12, 2008 5:29 pm
Sum of any 2 sides of a triangle has to be greater than the 3rd side.
2+5 is 7, if you subtract 7 from all the options to get the value of the 3rd side, you will get the answer, hope it helps
IMO A
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by LSB » Fri Sep 12, 2008 7:51 pm
Sunny22uk wrote:Sum of any 2 sides of a triangle has to be greater than the 3rd side.
2+5 is 7, if you subtract 7 from all the options to get the value of the 3rd side, you will get the answer, hope it helps
IMO A
The third side of a triangle must be less than the sum of the other two sides and greater than their difference.

Side 1: 5
Side 2: 2

Sum: 7
Difference: 3

The 3rd side: X

7 > X > 3

In this case the Perimeter must be between 10 (5+2+3) and 14 (5+2+7)

Ans E
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by Sunny22uk » Sat Sep 13, 2008 10:16 am
LSB wrote:
Sunny22uk wrote:Sum of any 2 sides of a triangle has to be greater than the 3rd side.
2+5 is 7, if you subtract 7 from all the options to get the value of the 3rd side, you will get the answer, hope it helps
IMO A
The third side of a triangle must be less than the sum of the other two sides and greater than their difference.

Side 1: 5
Side 2: 2

Sum: 7
Difference: 3

The 3rd side: X

7 > X > 3

In this case the Perimeter must be between 10 (5+2+3) and 14 (5+2+7)

Ans E
I have never heard of a rule which says that the the third side is greater than the other 2 side's difference. , One can easily disprove this "theorem", lets says three sides are 3,5,7. 7 is not greater than the difference of other 2 sides i.e. 2
Pick up O.G. and see a similar question no. 45 on page 158, you will get the answer for this question too.
Last edited by Sunny22uk on Sat Sep 13, 2008 10:23 am, edited 2 times in total.
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by Sunny22uk » Sat Sep 13, 2008 10:18 am
Oxana, Could you please post the OA for this question?
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by LSB » Sat Sep 13, 2008 4:34 pm
Sunny22uk wrote:lets says three sides are 3,5,7. 7 is not greater than the difference of other 2 sides i.e. 2
Not sure I understand your logic. How is 7 not greater than 2?

7 is greater than 5-3=2
5 is greater than 7-3=4
3 is greater than 7-5=2

Agree?
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by Sunny22uk » Sat Sep 13, 2008 5:17 pm
LSB wrote:
Sunny22uk wrote:lets says three sides are 3,5,7. 7 is not greater than the difference of other 2 sides i.e. 2
Not sure I understand your logic. How is 7 not greater than 2?

7 is greater than 5-3=2
5 is greater than 7-3=4
3 is greater than 7-5=2

Agree?
My apologies for the wrong pick of numbers, lets forget about the difference of 2 sides. We all know that sum of 2 triangles has to be greater than the 3rd side, Agree?
>>2,5 are the known sides
1) For 9 to be the perimeter, the 3rd side is 2. sum of 2 and 2 is not greater than 5.THIS CANNOT BE THE PERIMETER.
2) For 15 to be the perimeter,the 3rd side is 8, Sum of 2 and 5 is not greater than 8.THIS CANNOT BE THE PERIMETER.
3) For 12 to be the perimeter,the 3rd side is 12, Sum of 2 and 5 is not greater than 12.THIS CANNOT BE THE PERIMETER.
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by Sunny22uk » Sat Sep 13, 2008 5:31 pm
LSB wrote:
Sunny22uk wrote:Sum of any 2 sides of a triangle has to be greater than the 3rd side.
2+5 is 7, if you subtract 7 from all the options to get the value of the 3rd side, you will get the answer, hope it helps
IMO A
The third side of a triangle must be less than the sum of the other two sides and greater than their difference.

Side 1: 5
Side 2: 2

Sum: 7
Difference: 3

The 3rd side: X

7 > X > 3

In this case the Perimeter must be between 10 (5+2+3) and 14 (5+2+7)

Ans E
Your reasoning was right, but the answer is not E, it is A (none) as the perimeter is between 10 and 14(as you proved it yourself), the answer choices are 9,15,19.
I also did a quick analysis of "difference between 2 sides", it is indeed less than the 3rd side.
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by LSB » Sat Sep 13, 2008 5:31 pm
The answer is correct as is the approach. The approach is somewhat unintuitive to me (but everybody's head is wired differently).

Look into the difference rule though. You will find that you cannot pick any numbers that violate the rule. It may just make your life a bit easier if you have another rule in your pocket.
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by LSB » Sat Sep 13, 2008 5:34 pm
BTW - I just noticed that my original says Ans E. It is supposed to say Ans A ("None"). This answer is supported by my solution above.

Sorry for the confusion
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by LSB » Sat Sep 13, 2008 5:36 pm
Sunny22uk wrote:
LSB wrote:
Sunny22uk wrote:Sum of any 2 sides of a triangle has to be greater than the 3rd side.
2+5 is 7, if you subtract 7 from all the options to get the value of the 3rd side, you will get the answer, hope it helps
IMO A
The third side of a triangle must be less than the sum of the other two sides and greater than their difference.

Side 1: 5
Side 2: 2

Sum: 7
Difference: 3

The 3rd side: X

7 > X > 3

In this case the Perimeter must be between 10 (5+2+3) and 14 (5+2+7)

Ans E
Your reasoning was right, but the answer is not E, it is A (none) as the perimeter is between 10 and 14(as you proved it yourself), the answer choices are 9,15,19.
I also did a quick analysis of "difference between 2 sides", it is indeed less than the 3rd side.
I also just noticed this post. You caught the error. Thx :-)
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by Sunny22uk » Sat Sep 13, 2008 5:42 pm
LSB wrote:BTW - I just noticed that my original says Ans E. It is supposed to say Ans A ("None"). This answer is supported by my solution above.

Sorry for the confusion
and thanks for pointing the flaw in my example, I was high on crown royal at that time...lol
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