How often is a poll within its margin?

You will test the quick rule for the margin of luck. Your program runs many fair polls and counts how many land within the margin of the truth.

The idea. The quick rule says that about 95 fair polls in 100 land within $\dfrac{100}{\sqrt n}$ percentage points of the true percentage. Each person in a poll says yes with the chance $p$, the true share.

Your tasks.

1. Finish margin(n). Return the quick rule's margin in percentage points.
2. Finish poll(n, p). Ask n people at random, where each says yes with the chance p, and return the percentage who say yes.
3. Finish share_within(n, p, polls). Run polls polls and return the fraction of them that land within the margin of 100 * p.