Final answer:
The fraction of students who are now walkers is 2/5.
Step-by-step explanation:
In order to determine the fraction of students who are walkers after their number doubles, we need to first find the initial fraction of walkers.
The question tells us that 20% of Poe M.S. students walk to school, so the initial fraction of walkers is 20/100 or 1/5.
If the number of walkers doubles, the new fraction of walkers will be 2/5.
This is because doubling the number of walkers means they now make up 2 parts out of the total of 5 parts (2 out of 5 equals 2/5).
Therefore, the fraction of the students who are now walkers is 2/5.