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Each week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Explanations (OE) to them along with an alternate approaches if necessary.

We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button (the best solution we'll be put along the OE in the second post); 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Re: What is the perimeter of isosceles triangle MNP? [#permalink]
14 Jun 2012, 02:14

Expert's post

SOLUTION

What is the perimeter of isosceles triangle MNP?

(1) MN = 16. We only know the length of one side. Not sufficient. (2) NP = 20. We only know the length of one side. Not sufficient.

(1)+(2) If MN=MP=16 and NP=20 then the perimeter would be 16+16+20=52 but if MN=16 and NP=MP=20 then the perimeter would be 16+20+20=56. Not sufficient.

Re: What is the perimeter of isosceles triangle MNP? [#permalink]
14 Jun 2012, 03:38

1

This post received KUDOS

Bunuel wrote:

cyberjadugar wrote:

Hi,

Perimeter of isosceles triangle MNP?

Using (1), MN = 16, no idea about NP & MP. Insufficient.

Using (2) NP = 20, no idea about MN & MP. Insufficient.

Combining both the statements, MN = 16 & NP = 20 for MNP to be isosceles, the third side MP can be 16 or 20. Insufficient.

Thus, Answer is (E).

Regards,

Just a bit harder question, based on OG#28:

What is the perimeter of isosceles triangle MNP?

(1) MN = 16 (2) NP = 32

What would be the answer in this case?

Hi,

Using (1) & (2) alone we can't get the answer (similar to the explanation above)

Combinig (1) & (2), MN = 16 & NP = 32 Possible sides of triangle (16, 16, 32) & (16, 32, 32), now we know a+b>c (sum of two sides greater than third side) (16, 16, 32) doesn't fulfill this criteria Thus only possible triangle is (16, 32, 32) perimeter = 80

Re: What is the perimeter of isosceles triangle MNP? [#permalink]
14 Jun 2012, 03:46

Expert's post

cyberjadugar wrote:

Bunuel wrote:

cyberjadugar wrote:

Hi,

Perimeter of isosceles triangle MNP?

Using (1), MN = 16, no idea about NP & MP. Insufficient.

Using (2) NP = 20, no idea about MN & MP. Insufficient.

Combining both the statements, MN = 16 & NP = 20 for MNP to be isosceles, the third side MP can be 16 or 20. Insufficient.

Thus, Answer is (E).

Regards,

Just a bit harder question, based on OG#28:

What is the perimeter of isosceles triangle MNP?

(1) MN = 16 (2) NP = 32

What would be the answer in this case?

Hi,

Using (1) & (2) alone we can't get the answer (similar to the explanation above)

Combinig (1) & (2), MN = 16 & NP = 32 Possible sides of triangle (16, 16, 32) & (16, 32, 32), now we know a+b>c (sum of two sides greater than third side) (16, 16, 32) doesn't fulfill this criteria Thus only possible triangle is (16, 32, 32) perimeter = 80

Thus, Answer is (C)

Regards,

Correct.

What is the perimeter of isosceles triangle MNP?

(1) MN = 16 (2) NP = 32

MUST KNOW FOR THE GMAT: The length of any side of a triangle must be larger than the positive difference of the other two sides, but smaller than the sum of the other two sides.

When we consider the two statements together we can see that the case of {16, 16, 32} is not possible since the sum of two sides (16 and 16) is not greater then the third side (32), so only the following case is possible: {16, 32, 32}, which gives the perimeter equal to 16+32+32=80.

Re: What is the perimeter of isosceles triangle MNP? [#permalink]
16 Jun 2012, 04:15

Higher then 550 for sure. I think 600.

Unless we know the property "The length of any side of a triangle must be larger than the positive difference of the other two sides, but smaller than the sum of the other two sides", we can not answer the question easily.

Stmt 1: We can know the second side but don't know the length of third side. Stmt 2: Same logic as given for stmt 1.

Together the third side can be 16 or it can be 20 also.

Re: What is the perimeter of isosceles triangle MNP? [#permalink]
22 Jun 2012, 03:02

Expert's post

SOLUTION

What is the perimeter of isosceles triangle MNP?

(1) MN = 16. We only know the length of one side. Not sufficient. (2) NP = 20. We only know the length of one side. Not sufficient.

(1)+(2) If MN=MP=16 and NP=20 then the perimeter would be 16+16+20=52 but if MN=16 and NP=MP=20 then the perimeter would be 16+20+20=56. Not sufficient.

Re: What is the perimeter of isosceles triangle MNP? [#permalink]
23 Jul 2012, 06:47

What is the perimeter of isosceles triangle MNP? PERIMETER=MN+NP+MP Not given which sides are equal (1) MN = 16 NP&MP unavailable so insufficient (2) NP = 20 MN&MP unavailable so insufficient from (i)&(ii) Perimeter=MN+NP+MP=16+20+?, we don't know which two sides are equal;insufficient (E)
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