lazyashell wrote:
A certain code contains five letters, including one A, two B's, and two C's. In how many possible ways can we create the codes?
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When we want to arrange a group of items in which some of the items are identical, we can use something called the
MISSISSIPPI rule.
It goes like this:
If there are n objects where A of them are alike, another B of them are alike, another C of them are alike, and so on, then the total number of possible arrangements = n!/[(A!)(B!)(C!)....] So, for example, we can calculate the number of arrangements of the letters in MISSISSIPPI as follows:
There are
11 letters in total
There are
4 identical I's
There are
4 identical S's
There are
2 identical P's
So, the total number of possible arrangements =
11!/[(
4!)(
4!)(
2!)]
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In the given question, we want to arrange the following: A, B, B, C, C
There are
5 letters in total
There are
2 identical B's
There are
2 identical C's
So, the total number of possible arrangements =
5!/[(
2!)(
2!) = 30
Answer: 30
Cheers,
Brent