Final answer:
Angie painted 1/5 of a fence in one hour, so it will take her 5 hours to paint one full fence.
Step-by-step explanation:
The question asks how long it will take Angie to paint one fence if she has painted four twentieths (4/20) of a fence in one hour. To find the time necessary for one whole fence, you can establish a proportion based on the part of the fence painted in a given time. Angie paints 4/20 of a fence in 1 hour, which simplifies to painting 1/5 of a fence in 1 hour because 4/20 reduces to 1/5. To paint a whole fence (which is 5/5 or 1), it would take 5 times the amount of time, since 1 (whole fence) divided by 1/5 (part painted per hour) equals 5. Therefore, it will take Angie 5 hours to paint one full fence.