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Door secret code...permutation
A secret code that needs to be key-ed in using only 1,2,3,4,5 button. If to open the door, u need to press three buttons, how many possible ways there to open the door? Assume tat the same code may be repeated.
Re: Door secret code...permutation
If the code can be repeated, then the answer is 5³ as you say.
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman