What is the perimeter of isosceles triangle LMN?

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Vincen: Legendary Member; Posts: 2898; Joined: Thu Sep 07, 2017 2:49 pmFollowed by: 5 members; Thanked: 6 times

by Vincen » Fri Sep 29, 2017 6:24 pm

What is the perimeter of isosceles triangle LMN?

1) Side LM has a length of 4

(2) Side MN has a length of 4âˆš2.

The OA is E.

If we use both statements together we can find the perimeter of the triangle. Am I wrong?

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Source: Beat The GMAT — Data Sufficiency | Fri Sep 29, 2017 6:24 pm

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ErikaPrepScholar: Legendary Member; Posts: 503; Joined: Thu Jul 20, 2017 9:03 amFollowed by: 15 members; Thanked: 86 times; GMAT Score:770

by ErikaPrepScholar » Wed Oct 11, 2017 8:44 am

Hey Vincen,

The big issue here is that we know that the triangle is isosceles, but we don't know which two sides are the same. We know with both statements that LM and MN are different. But we don't know whether LN is the same length as LM (4) or the same length as MN (4âˆš2). If LN and LM are the same, the perimeter is 4 + 4 + 4âˆš2. If LN and MN are the same, the perimeter is 4 + 4âˆš2 + 4 âˆš2. Not the same.

So even with both statements, we don't know the perimeter of the triangle.

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