Thursday Password Cracking Homework

Imagine a lock with a 4 digit passcode:

Now imagine that you have some fancy spy technology and you can put on some goggles and see which keys have been pressed, but not the order, or number of times they were pressed. If you see this, how many possible passcodes are there?

Homework:

What if two keys have been pressed? Three?

Comments

Quantum Dranger said…

1 digits: 1
2 digits: 2^4-2
3 digits: 3^4-3-3*14
4 digits: 4*3*2*1 = 24

February 22, 2016 at 9:17 AM

Quantum Dranger said…

Also X factorial over X factorial minus number of slots.

February 22, 2016 at 9:20 AM

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