part 2: https://codeforces.com/blog/entry/62792
Watch my lecture-stream tomorrow (Thursday) at 14:00 CEST — https://www.youtube.com/watch?v=qdlPY37MBPo https://www.youtube.com/watch?v=U_h3IjreRek. I will go through theory and problems from this blog. The only prerequisite is knowing what is probability. The next (harder) part on Monday.
The video will be available later, with timestamps for each problem — so you don't have to watch everything.
Definition of EV
Let's say we bought a lottery ticket for 2$. We will win 10$ with probability 10%, and 20$ with p-bility 2%. On average, it gives us 0.1·10 + 0.02·20 = 1.4, so we are worse off after buying the ticket. The computed average is called the expected value.
The expected value (EV, expectation) is the average value of an event/experiment. For example, EV of the number of pips rolled on a 6-sided die is 3.5:
Linearity of EV (super important theorem):