Math CentralQuandaries & Queries


Question from Amanda, a student:

okay so i forgot my lock code for my phone its four digits but i know it doesn't have a 1 or a 0 in it so it has to be from numbers 2 to 9 i need to know all the four digit combinations asap cause i cant use my phone till can someone please help me Amanda


there are 8 × 8 × 8 × 8 possibilities; that's 4096 possibilities and if you have no other clues about it there not much you can do but start trying them all. If, or example you recall that the digits were distinct then there are only 8 × 7 × 6 × 5 = 1680 possibilities.

It would be best to try all the possibilities it in a logical way, say starting from the smallest, 2222, and working your way up.

2222, 2223, 2224, ... 2229, 2232, 2233, ...

Have fun,


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