Using Small Examples to Solve Combinatorial Problems

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Discussion Overview

The discussion revolves around the methods used to solve combinatorial problems, specifically focusing on counting factors in factorials. Participants explore the reasoning behind using smaller examples to understand larger problems, particularly in the context of counting prime factors in factorials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the rationale behind dividing 50 by powers of 2 and 3, seeking clarity on the relationship between 50 and 50!.
  • Another participant suggests that the method is fundamentally about counting factors, though they express uncertainty about the original poster's understanding.
  • A participant reflects on their initial overcomplication of the problem and requests a simpler explanation from the beginning.
  • Several participants provide a detailed breakdown of counting factors of 2 in 10!, illustrating the process and arriving at the conclusion that 10! has eight factors of 2.
  • One participant emphasizes the value of using smaller examples to grasp larger problems, particularly in combinatorial contexts, and notes that this approach can help verify general formulas.

Areas of Agreement / Disagreement

Participants generally agree on the utility of using smaller examples to understand combinatorial problems, but there is no consensus on the specific reasoning behind the choice of methods or the initial question regarding the division by powers of 2 and 3.

Contextual Notes

The discussion includes varying levels of understanding among participants, with some expressing confusion and others providing detailed explanations. There are also repeated claims about counting factors without resolving the initial question posed.

sahilmm15
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In the below picture I understood the problem and also understood the solution. But I am not clear on why did they choose this particular method. So my question is why did they divided 50 with powers of 2 and 3, and what relation does ##50## have with ##50!## ( I am clear on the solution part but I am clueless how would have the author thought of the problem.) Thanks!
IMG_20201224_143619.jpg
 
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It's just counting factors isn't it? It's not clear how much you understand.
 
PeroK said:
It's just counting factors isn't it? It's not clear how much you understand.
I think I overcomplicated it. Can you explain me from scratch.
 
sahilmm15 said:
I think I overcomplicated it. Can you explain me from scratch.
If you look at ##10!## say, then count the factors of ##2##. We have:

2, 4, 6, 8 and 10 all have a factor of 2 (that's five factors of 2)

4 and 8 have a second factor of 2 (that's two more factors of 2)

8 has a third factor of 2 (that's another one)

Altogether, therefore, ##10!## has eight factors of 2. And doing this for the other primes we see that: $$10! = 2^8 \times 3^4 \times 5^2 \times 7$$
 
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PeroK said:
If you look at ##10!## say, then count the factors of ##2##. We have:

2, 4, 6, 8 and 10 all have a factor of 2 (that's five factors of 2)

4 and 8 have a second factor of 2 (that's two more factors of 2)

8 has a third factor of 2 (that's another one)

Altogether, therefore, ##10!## has eight factors of 2. And doing this for the other primes we see that: $$10! = 2^8 \times 3^4 \times 5^2 \times 7$$
This was so simple. Thanks!
 
PeroK said:
If you look at ##10!## say, then count the factors of ##2##. We have:

2, 4, 6, 8 and 10 all have a factor of 2 (that's five factors of 2)

4 and 8 have a second factor of 2 (that's two more factors of 2)

8 has a third factor of 2 (that's another one)

Altogether, therefore, ##10!## has eight factors of 2. And doing this for the other primes we see that: $$10! = 2^8 \times 3^4 \times 5^2 \times 7$$
What I learned from this example is if you cannot comprehend a bigger problem take a smaller example and relate to the steps. I saw you doing this from past 2 answers and it worked beautifully.
 
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sahilmm15 said:
What I learned from this example is if you cannot comprehend a bigger problem take a smaller example and relate to the steps. I saw you doing this from past 2 answers and it worked beautifully.
Especially for these combinatorial problems. If in doubt, count for a low-value example. Often that's how you see what's going.

And, it gives you an answer to check against any general formula you come up with.
 
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