: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
prep test 1
This topic has expert replies
Source: Beat The GMAT — Problem Solving |
-
LSB
- Master | Next Rank: 500 Posts
- Posts: 229
- Joined: Thu Nov 08, 2007 3:47 pm
- Thanked: 14 times
- GMAT Score:750
The third side of a triangle must be less than the sum of the other two sides and greater than their difference.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
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
-
Sunny22uk
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Thu Apr 17, 2008 3:33 pm
- Thanked: 8 times
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. 2LSB wrote:The third side of a triangle must be less than the sum of the other two sides and greater than their difference.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
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
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.
You cannot discover new oceans unless you have the courage to loose sight of the shore.
-
LSB
- Master | Next Rank: 500 Posts
- Posts: 229
- Joined: Thu Nov 08, 2007 3:47 pm
- Thanked: 14 times
- GMAT Score:750
Not sure I understand your logic. How is 7 not greater than 2?Sunny22uk wrote:lets says three sides are 3,5,7. 7 is not greater than the difference of other 2 sides i.e. 2
7 is greater than 5-3=2
5 is greater than 7-3=4
3 is greater than 7-5=2
Agree?
-
Sunny22uk
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Thu Apr 17, 2008 3:33 pm
- Thanked: 8 times
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?LSB wrote:Not sure I understand your logic. How is 7 not greater than 2?Sunny22uk wrote:lets says three sides are 3,5,7. 7 is not greater than the difference of other 2 sides i.e. 2
7 is greater than 5-3=2
5 is greater than 7-3=4
3 is greater than 7-5=2
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.
You cannot discover new oceans unless you have the courage to loose sight of the shore.
-
Sunny22uk
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Thu Apr 17, 2008 3:33 pm
- Thanked: 8 times
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.LSB wrote:The third side of a triangle must be less than the sum of the other two sides and greater than their difference.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
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 also did a quick analysis of "difference between 2 sides", it is indeed less than the 3rd side.
You cannot discover new oceans unless you have the courage to loose sight of the shore.
-
LSB
- Master | Next Rank: 500 Posts
- Posts: 229
- Joined: Thu Nov 08, 2007 3:47 pm
- Thanked: 14 times
- GMAT Score:750
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.
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.
-
LSB
- Master | Next Rank: 500 Posts
- Posts: 229
- Joined: Thu Nov 08, 2007 3:47 pm
- Thanked: 14 times
- GMAT Score:750
I also just noticed this post. You caught the error. ThxSunny22uk wrote: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.LSB wrote:The third side of a triangle must be less than the sum of the other two sides and greater than their difference.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
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 also did a quick analysis of "difference between 2 sides", it is indeed less than the 3rd side.
-
Sunny22uk
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Thu Apr 17, 2008 3:33 pm
- Thanked: 8 times
and thanks for pointing the flaw in my example, I was high on crown royal at that time...lolLSB 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
You cannot discover new oceans unless you have the courage to loose sight of the shore.
