Pretest
Have a go before we teach it — wrong is fine, and it helps.
A padlock code consists of 4 digits, each drawn uniformly from {0,1,...,9} independently of the others. What is the probability that at least two of the four digits are equal?
Pretest
Have a go before we teach it — wrong is fine, and it helps.
A padlock code consists of 4 digits, each drawn uniformly from {0,1,...,9} independently of the others. What is the probability that at least two of the four digits are equal?