Find the sides of an isosceles triangle whose base is 30% of the side and the perimeter is 69 cm.

1. Let’s denote the sought-for lateral side of an isosceles triangle by b, the base by a.

2. By the condition of the problem, it is known that the length of the base a is 30% of the length b, that is

a = b * 30: 100 = 0.3 b.

3. Let’s make an equation, since we know that the perimeter P of a given triangle is 69 cm.

P = 2 * b + 0.3 b = 69 cm;

2.3 b = 69 cm;

b = 69: 2.3 = 30 cm.

4. Let’s calculate what is the base length a.

a = 0.3 b = 0.3 * 30 = 10 cm.

Answer: The length of the side of the triangle is 30 cm, the length of the base is 10 cm.