Daniel wanted to make note cards by cutting pieces of paper in half. Before starting he got three more pieces to use. When he had 20 half-pieces of paper. With how many did he start with? ( I need the step by step how to solve this)

How do you find p(a and b) if a and b are independent events for two or more actions, such as tossing a coin twice and finding p(heads and heads)? 2. how do you find p(a or b) if a and b are independent events for one action, such as spinning a four-color spinner once and finding p(red or blue)?