Exercise 3 solution

Sample answers (yours may differ):
Zip pull cord - overhand: small, quick, and the cord is not under heavy load.
Blind cord end - figure-eight: larger, so it will not pull through the guide, and easy to untie later.
Washing line or bucket rope end - figure-eight: stops the end slipping through a post hole or ring.
Reasoning: choose the overhand for light, quick, low-stakes jobs; choose the figure-eight when the knot will be loaded or must be untied again.