Question from Perms and Combs unit

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In summary, the conversation discusses the process of finding the number of 5-letter words that can be formed from the letters in the word "ELEMENTS" where vowels and consonants alternate. The solution involves using cases and correctly accounting for the repeated letter "E". The final answer is 80, as confirmed by the conversation.
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Homework Statement


Given the letters of the word ELEMENTS, how many 5 letter "words" can be found in which vowels and consonants alternate


Homework Equations





The Attempt at a Solution


I see the need to use Cases here because the pattern can either go:

v c v c v

or

c v c v c

So I did:

Case 1 : vowel starts 3 5 2 4 1 = 120
Case 2: consonant starts 5 3 4 2 3 = 360

Add them up to get 480, however the answer says 80. What went wrong? Or was that a typo mistake?
 
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  • #2
Is there any difference between the first and last E?
 
  • #3
Don't think so.
 
  • #4
So how many different ways are there to arrange the vowels?
 
  • #5
Nevermind, I found out what I did wrong, I forgot to divide each case by 3! for the repetitive E's.
 
  • #6
What do you mean "nevermind", that was what Nate was pointing out all along.
 

Related to Question from Perms and Combs unit

1. How do I know when to use permutations or combinations?

Permutations are used when the order of items matters, such as arranging letters in a word. Combinations are used when the order does not matter, such as choosing toppings for a pizza.

2. Can you give an example of solving a permutation problem?

Sure, let's say you have 5 different colored balloons and want to know how many ways you can arrange them in a line. This would be a permutation problem because the order of the balloons matters. The formula for permutations is n! / (n-r)! where n is the total number of items and r is the number of items being chosen. In this case, it would be 5! / (5-5)! = 5! / 0! = 5 x 4 x 3 x 2 x 1 = 120. So there are 120 ways to arrange the balloons in a line.

3. How do I solve a combination problem?

To solve a combination problem, you can use the formula nCr = n! / r!(n-r)! where n is the total number of items and r is the number of items being chosen. For example, if you have 10 different flavors of ice cream and want to choose 3 flavors for a sundae, the formula would be 10C3 = 10! / 3!(10-3)! = 10! / 3!7! = 10 x 9 x 8 / 3 x 2 x 1 = 120. So there are 120 different combinations of 3 flavors for your sundae.

4. Can permutations and combinations be used in real-life situations?

Absolutely! Permutations and combinations are used in various fields such as mathematics, science, computer science, and business. For example, calculating the number of possible combinations of passwords, arranging elements in a chemical compound, or choosing lottery numbers are all situations where permutations and combinations can be applied.

5. Is there an easy way to remember the difference between permutations and combinations?

One way to remember the difference is to think of a combination lock. The order of numbers in the combination does not matter, so it is a combination. Permutations, on the other hand, are like arranging items in a line, where the order does matter. Another way is to remember the formula for permutations (n! / (n-r)!) and combinations (nCr = n! / r!(n-r)!).

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