first let me explain the title
for positive integer n, n! = 1x2x3x...xn e.g. 3! = 1x2x3 = 6
although my mum never did excel academically, i bet she was at least good at Math, in particular, permutations involving 4 digits, with or without repetition.
recently she called me (which is rare ever since i set up the monthly auto funds transfer to her account... she used to call me EVERY month, "coincidentally" near pay day -.-||| sadz.... sighs... )
tru tru tru....
mum: girl ah, ler gai seng chia number gwee hor? (girl ah, what's your new car plate number?)
me: *roll eye balls* er.. XYZZ
mum: HA??? ah ya, wa sior ta si ZYXX!!! ah ya... (HA??? i thought it's ZYXX!!! ah ya...
me: er... ler ai boi 4D -.- (er... you want to buy 4D)
mum: ah ya! uncle dah salah! (ah ya, uncle say wrongly!)
and i bet she will buy all 4!/2! = 12 permutations of that number -___________-|||
i always tell her if she saved that money, she'd probably end up with more... i shudder to think what will happen when the IRs come up... it's really difficult trying to explain Gambler's Ruin problem to mum >.< i'll just have to pray for her...