Final answer:
The remaining exterior angle of the isosceles triangle is 120°, therefore the associated interior angle is 60°, and the triangle is equilateral with all interior angles being 60°.
Step-by-step explanation:
The sum of the exterior angles of a triangle is always equal to 360°. Given that the sum of two exterior angles is 240°, the remaining exterior angle must be 120° (since 360° - 240° = 120°). The interior angle is supplementary to the exterior angle in a triangle, meaning they add up to 180°. Therefore, the measure of the associated interior angle is 60° (since 180° - 120° = 60°). Because the triangle is isosceles, two of its interior angles are equal. The two equal interior angles are each 60°, and the third interior angle would be the one supplementary to the sum of the other two. This results in the third angle also being 60°, thus making the triangle equilateral as all interior angles are equal.