Today's coin flip remembers nothing of yesterday's, so when events don't affect each other you just multiply, P(A∩B) = P(A)P(B)
Module goal. Tell apart "they don't affect each other" from "knowing one, now look at the other," and master the multiplication, conditional, and total probability rules
eastmath.com · 33.4 Independence and Conditional Probability · 33.4.1 Independent Events