The perimeter of an isosceles triangle is 1m, and the base is 0.4m. Find the length of the side.

Let us denote by the variable x the number of meters, which corresponds to the length of the lateral side of the specified isosceles triangle (by definition, the lengths of the lateral sides of this type of triangles are equal).
Knowing by the condition of the problem that the perimeter of a triangle is 1 meter, with a base length equal to 0.4 meters, we compose an equation and determine the length of the lateral side of the specified isosceles triangle:
x + x + 0.4 = 1;
2x = 0.6;
x = 0.3.
Answer: The length of the side of the triangle is 0.3 meters.