What is the total number of combinations of letters in the word MISSISSIPPI?

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Discussion Overview

The discussion revolves around calculating the total number of combinations of letters that can be formed from the word "MISSISSIPPI". Participants explore the interpretation of the question, the methodology for counting combinations, and the implications of different approaches to the problem.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about the question and provides an initial calculation using the formula for combinations, which does not match the expected answer.
  • Another participant clarifies that the question requires counting all possible combinations of one or more letters, not just the full 11-letter combination.
  • Some participants question whether different arrangements of the same letters (e.g., "MISSISSIPPI" vs. "IIIIMPPSSSS") should be considered distinct combinations or not.
  • A participant suggests looking at smaller cases to identify patterns in combinations, using examples like "AAA" and "ABC".
  • One participant proposes a generating function approach to calculate the combinations, arriving at the answer of 149, while another expresses concern about the complexity of this method.
  • There are discussions about the appropriateness of the methods used and whether simpler approaches could yield the same result more efficiently.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method for calculating the combinations, and there are multiple interpretations of the problem. Some participants agree on the need to count combinations of varying lengths, while others debate the complexity of different approaches.

Contextual Notes

Some participants express uncertainty about the definitions and assumptions underlying the problem, particularly regarding what constitutes a valid combination and how to handle repeated letters.

Who May Find This Useful

This discussion may be useful for individuals interested in combinatorial mathematics, particularly those exploring problems involving multisets and combinations of letters.

Suyash Singh
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The total number of different combinations of one or more letters which can be made from the letters of the word MISSISSIPPI is?

First i don't understand what the question means
and second my answer is completely different from that in my book

My working-
since there are 11 letter 4 I 4 S 2 P
Number of combinations= (11!) /(4! 4! 2!)
But this is not even close to the answer.
 
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It says, "of one or more letters". So you need to count all of the one letter combinations, the two letter combinations, the three letter combinations, and so on, then add them all up. You only counted the 11 letter combinations.
 
I'm not sure how to interpret combinations here.
Are MISSISSIPPI and IIIIMPPSSSS different combinations, or are they different ways to describe the same combination "take all 11 letters"?
The first interpretation makes the problem very messy casework, the second one has a short solution.
 
mfb said:
I'm not sure how to interpret combinations here.
Are MISSISSIPPI and IIIIMPPSSSS different combinations, or are they different ways to describe the same combination "take all 11 letters"?
The first interpretation makes the problem very messy casework, the second one has a short solution.
the answer is 149
 
The second interpretation then.
"Take all 11 letters" is one case. "Take all apart from the M" is another, and so on.

If you don't know how to start, it is always useful to look at smaller cases.

How many options are there for "AAA" or "AAAA"? What about "ABC"? "AAABBB"? Do you see some pattern?
 
Still can't understand anything :(
 
something like 1 letter combinations then 2 letter then so on?
 
Yes.

As an example, for "AAA" there are the combinations "A", "AA" and "AAA". The combination "" doesn't have any letter so it doesn't count. What about the other examples I mentioned?
 
ok so like this
there are 2p 4iand 4s

2+4+4+1!+2!+3!+4! (cause 4 different letters)

=43 oops
 
  • #10
Suyash Singh said:
Still can't understand anything :(

Given the eleven letters MISSISSIPPI can you make the following words?

RIVER
MIPS
PIPPI
X
IS

Some yes, some no. So, how many words can you make in total?

Ah, I see that's not the question! I guess permutations would be words.
 
Last edited:
  • #11
Suyash Singh said:
ok so like this
there are 2p 4iand 4s

2+4+4+1!+2!+3!+4! (cause 4 different letters)

=43 oops
See above: Start with easier cases to see how it works.
 
  • #12
Suyash Singh said:
The total number of different combinations of one or more letters which can be made from the letters of the word MISSISSIPPI is?

First i don't understand what the question means
and second my answer is completely different from that in my book

My working-
since there are 11 letter 4 I 4 S 2 P
Number of combinations= (11!) /(4! 4! 2!)
But this is not even close to the answer.
What is the answer in your book ?
 
  • #13
T13091999 said:
What is the answer in your book ?
149
 
  • #14
Suyash Singh said:
The total number of different combinations of one or more letters which can be made from the letters of the word MISSISSIPPI is?

First i don't understand what the question means
and second my answer is completely different from that in my book

My working-
since there are 11 letter 4 I 4 S 2 P
Number of combinations= (11!) /(4! 4! 2!)
But this is not even close to the answer.
OK. I've got the answer.
We have the multiset
$$\left\{\text{M}^1, \, \text{I}^4,\, \text{S}^4,\, \text{P}^2\right\}\tag*{}$$
Now, we can form the combination generating function by assuming each letter to be x.
$$(1+x)(1+x+x^2+x^3+x^4)^2(1+x+x^2)$$
$$=x^{11}+4x^{10}+9x^9+15x^8+21x^7+25x^6+25x^5+21x^4+15x^3+9x^2+4x+1$$
Now, add the coefficients except the constant term. You'll get 149.
Read this if you want to clear your understanding.
https://www.quora.com/How-can-I-fin...INATION-taking-4-at-a-time/answer/Nick-Shales
 
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  • #15
@T13091999: While that is not impossible, it is like calculating 4+7 with Fourier transformations. It is way more complicated than necessary.
In addition, it is OP's homework, not yours.
 
  • #16
mfb said:
@T13091999: While that is not impossible, it is like calculating 4+7 with Fourier transformations. It is way more complicated than necessary.
In addition, it is OP's homework, not yours.
I was just trying to help. I got the answer. Still, I am not happy with my way of doing it. Do you have any sugesstion ?
P.S. : I did the sum as I was trying to help the OP.
 
  • #17
I liked the question, has this been posted here from another forum in order to engage more people?
 
  • #18
T13091999 said:
Do you have any sugesstion ?
Post #5 should help enough to find a short, easy, general formula. With the right approach can calculate the answer in your head in a few seconds.
 
  • #19
T13091999 said:
Still, I am not happy with my way of doing it. Do you have any sugesstion ?

Think of it like this. Someone has four bags, and each bag contains tiles with one letter on them. One is a bag of M's, another a bag of I's etc. (For the general problem you can imagine 26 bags each containing tiles with one letter.)

You want to make a combination of some or all of the letters in Mississippi. You need to get your letters from the person with the bags of letters. What do you ask for?
 
  • #20
mfb said:
Post #5 should help enough to find a short, easy, general formula. With the right approach can calculate the answer in your head in a few seconds.
Seems like I killed the mosquito with my machine gun.
$$\Large \ddot \smile$$
 
  • #21
I actually liked what came at the end of "a hail of bullets". Something to get to grips with before senescence takes its ugly grip.
 

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