The measure of one of the exterior angles of a triangle is twice one of the interior opposite angles and the measure of the other interior opposite angles is 60° . The triangle is a/an:

equilateral triangle

Let one of the interior opposites angles = a

The measure of one of the exterior angle = a + 60° 

According to the question,

⇒ 2 × one of the interior opposite angles = a + 60° 

⇒ 2a = a + 60° 

⇒ 2a - a = 60° 

⇒ a = 60° 

Now the third interior angle = 180° - a - 60°  = 180° - 60° - 60° = 60° 

Now, if all the angles are same and of 60^o then we can say that it is a equilateral triangle.