In triangle ABC, AB = AC = 25 and BC = 20. Points D, E and F are on sides AB, BC and AC respectively, such that DE and EF are parallel to AC and AB respectively. What is the perimeter of parallelogram ADEF?
EFC is an isosceles triangle. So AF + EF will equal one of the larger sides of the biggest triangle. Since it is a parallelogram, the same holds true for AD+DE. So AC is 25 and 25+25=50.