March 2021

$f(x) = \dfrac{1}{\sigma \sqrt{2\pi}} e^{-\frac{1}{2} \left( \frac{x - \mu}{\sigma} \right)^2}$

$z = \dfrac{x - \mu}{\sigma}$
 

Binomial Probability Distribution Formula
$ P(x) = p^x \, q^{n - x} \, {_n}C_x $

$P(E)=\dfrac{\text{number of outcomes in }E}{\text{size of sample space}}$

Permutation
$P(n, ~ r) = \dfrac{n!}{(n - r)!}$
 

Combination
$C(n, ~ r) = \dfrac{n!}{r! \, (n - r)!}$
 

Fundamental Principle of Counting

If there are $m$ ways to do a task and $n$ ways to do another task, the number of ways to do the first then the second task is $m \times n$.
 

Digit-related, Money-related, etc.