It just occurred to me to revise what one has learned in factorials, permutations and combinations long ago.
I developed some snippet code, mainly to answer one of the questions, that if my passcode/pin in my ATM has 4 slots for 10 different digits to be inserted, how many possibilities could be there before finding the right number.
Again I’m not a mathematician, just revising the math rules and putting them in some code using HMTL, JQuery and CSS.
Here’s the link to my code: http://jsfiddle.net/joeSaad/bXy6a/#base
Let me know if you would like to add more for understanding anything more about these rules.