Don't understand what part b is asking me?

[topaz urchin]

So for part a, I got that there are P(7,4) possible 4 digit numbers that can be made with those digits, but part b is asking me to find how many have no repeated digits? except that none of the numbers have repeated digits don't they? no number will have two 1s or two 8s since they're used once in each 4digit number

[barren abyss]

1. Ask your question and show the work you've done so far. If you've posted a screenshot of a question, specify which part you need help with.
2. Wait patiently for a helper to come along.
3. Once someone helps you, say thank you and close the thread with:

   +close
   

4. Feel free to nominate the person for helper of the week in #helper-nominations
5. Do not ping the mods, unless someone is breaking the rules.
6. If you're happy with the help you got here, and the server overall, you can contribute financially as well:

[bronze barn]

The answer you tried to get is already for (b). Note, however, that you didn't account for the fact that the number can't start with a 0.

[topaz urchin]

oh yeah ur right, forgot about starting with 0 😔

so is the answer for (b) the same as the answer for (a), since there aren't any four digit numbers with repeated digit

answer for (a) being total combinations minus the ones that start with 0

[bronze barn]

Well, no. As we can repeat digits, the number of choices for each position in (a) is the same (except the first position can't be 0, so it's 1 less).

[topaz urchin]

oh

so would the answer in (a) be

6*7^3

6 is the amount of digits there are without 0s

and there's 7 digits

6 7 7 7

so (a): 6*7^3 and
(b): P(7,4)-P(6,3)

is this correct?

[bronze barn]

In (b) you can also express it as 6A(6, 3). Though, of course, that's just a particular case of the identity A(n + 1, k + 1) = (n + 1)A(n, k).

[topaz urchin]

what is A? what does the 6A(6,3) mean

[bronze barn]

Same as what you mean by P. I just don't like using P for arrangements, only for permutations.
And 6A(6, 3) means just what it says: 6*6!/(6 - 3)!.

Again, because A(n + 1, k + 1) = (n + 1)A(n, k).

[topaz urchin]

Alright I think I get it, I'll have to look into that property though cause I've never seen it before

thank!

[bronze barn]

You're welcome!

[topaz urchin]

also who is fibonacci

[bronze barn]

And that property is pretty easy to derive.

[topaz urchin]

is it a bot

[bronze barn]

Yeah.

[topaz urchin]

what caused the reaction?

[bronze barn]

Honestly, not sure.

[topaz urchin]

oh ok 😂

well thanks anyways

cya

+close