Let’s assume, you are in a rush and you need a random number: What is the best way to produce a high-quality, uniformly distributed random integer number between 0 and 9, ideally using only mental math or, less ideally, tools that are commonly available (except for computers, calculators, smartphones and books, of course).
Toss a fair coin four times. Put a 1 if the toss is a head and a 0 otherwise. Make the four tosses into a string of 0s and 1s of length 4. For example you might get 0110. Convert this binary number to decimal; in the example you got 6. Toss it out and try again if the number is > 9.