This data sufficiency question asks the following: "If the area of triangular region RST is 25, what is the perimeter of RST?"

(1) The length of one side of RST is 5√2.
(2) RST is a right isosceles triangle.

The correct answer is B, because you are given an area of the triangle and you have two sides that are identical according to the definition of an isosceles triangle. Could you explain what the solution is trying to attempt with statement one ? I simply negated the sufficiency of the first statement, because we can be presented with many different types of triangles.

They're trying to trick you into thinking you don't have enough information from 2 and that you need 1 as well.
You noticed correctly that we can find the sides of an isosceles triangle if we're given the perimeter.
If we know that it's an isosceles triangle, though, we know that the sides are in the ratio x:x:x√2 and some students will believe that the 5√2 in 1 is necessary to solve the question.

Does this answer your question?

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