You can put this solution on YOUR website! This is a combination problem. Really you are looking for how many options do you have at each spot. Your "code" has 4 spots open:
(__-__-__-__)
And you just need to know if there are any limitations on them. The problem doesn't say you can't reuse a number, so you have 10 options for each spot.
(10-10-10-10)
To figure out how many different codes you could make, multiply the spots together.
.
.
If you run across a problem where you cannot reuse the numbers, here's what you'd do. You would have 10 numbers for the 1st slot, but only 9 for the second (since you used one of them in the first slot), then 8 for the 3rd, etc. To solve a problem like this, do the same thing:
(10-9-8-7)
And multiply together.
Future problem solved!
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