Solving a Practice Exam Question: Arranging Letters in ROCKET

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Discussion Overview

The discussion revolves around a practice exam question regarding the arrangement of letters in the word "ROCKET" with the condition that the vowels must always be together. Participants explore the combinatorial reasoning behind the calculation of arrangements.

Discussion Character

  • Mathematical reasoning
  • Homework-related
  • Conceptual clarification

Main Points Raised

  • One participant states that the answer to the arrangement problem is 5! x 2, questioning the use of 5 instead of 4, given that two vowels are selected.
  • Another participant explains that the vowels E and O can be treated as a single unit or "letter," leading to the arrangement of five units (R, OE, C, K, T) resulting in 5! arrangements.
  • A subsequent reply suggests that the arrangement of the vowels can be represented as either "eo" or "oe," contributing the factor of 2 to the total arrangements.
  • Further discussion includes a simplification of the letter pairs as "P" for clarity, while questioning the overall logic of the arrangement process.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the reasoning behind the factorial calculations, with some agreeing on the treatment of vowels as a pair while others seek clarification on the logic used.

Contextual Notes

There is a lack of consensus on the reasoning behind the choice of 5! versus 4!, and the discussion includes assumptions about treating vowels as a single unit without fully resolving the implications of this approach.

nari
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Hi! There is this question in my practice exam:

How many ways can all the letters in the word ROCKET be arranged so that the vowels are always together?

The answer is 5! x 2.

I understand where the 2 is coming from. What I don't understand is the 5. Shouldn't it be 4!, since we already selected two out of six letters?
 
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nari said:
Hi! There is this question in my practice exam:

How many ways can all the letters in the word ROCKET be arranged so that the vowels are always together?

The answer is 5! x 2.

I understand where the 2 is coming from. What I don't understand is the 5. Shouldn't it be 4!, since we already selected two out of six letters?
Think of the E and the O as being glued together. They then count as a single "letter", and you have 5! ways of arranging the five letters R OE C K and T. The 2 just tells you whether the E comes before or after the O.
 
Opalg said:
Think of the E and the O as being glued together. They then count as a single "letter", and you have 5! ways of arranging the five letters R OE C K and T. The 2 just tells you whether the E comes before or after the O.

So then the options would be: eo/oe + r o/e c k t?
 
nari said:
So then the options would be: eo/oe + r o/e c k t?

I don't quite follow the whole logic here but the beginning part is true, the letter pairs are "eo" or "oe". For simplicity let's just called these two letters P (for pair). Opalg suggested the same thing but maybe seeing it like this will help.

How many ways can you arrange RPCKT?
 

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