Statistics Telecoms Line.

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Alan1990

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Mar 23, 2020
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Hey Guys.

I am just doing my maths assignment for engineering ACCESS and it has a problem in I am really confused on related to combinations. Unfortunately I've had no teaching on this due to corona and I feel like the question is worded really weirdly, though it may just be me.

The questions says:

One telecommunication like consists of two wires that are twisted together, known as a "pair". This pair of wires cannot be separated and can be used for transmitting or receiving but not both. A telecom link consists of one pair for the transmit direction and one pair for the receive direction. How many possible link combinations can be achieved using a cable consisting of 100 pairs?



I just don't understand it. I think I would get it if it just said 100 wires connect to 100 wires, how many combinations will there be. But since it says each wire has 2 little wires called a pair coming from it, then does that mean that one pair linked to another pair has 1 combination or 2? I am so confused, any help would be much appreciated.

Thanks in advance.
 
They are asking for the number of ways to split 100 elements into 2-element subsets.
 
I see, I'll try reading about sub sets. I've only just learned about combinations. Like how many ways to pick 3 marbles from a hat and what the difference is between permutations and combinations.

Thanks for the tip, do you know of any videos or guides that would be able to explain it to me? Feel so confused right now ??
 
Any introductory book or online lecture notes on combinatorics.
 
Ah combinatorics thanks. Had no idea what I was meant to be searching for but I think knowing the subject name will help.
 
No, the answer is different. You have to split the whole 100-element data set into pairs.
 
You don't have time to guide me through doing that do you? I am still looking at the combinatorics but I'm just not getting how to do it yet. My assignment is due Tuesday and can't ask the teacher because of crappy Corona.
 
I did guide you. You should not be "looking through" combinatorics. You should read the combinatorics notes/sections and memorize the most important formulas. I gave you all the hints. The only bigger thing would be giving you the actual formula of the solution.
 
Alan, on this forum we prefer to let the student solve their own problem instead of just giving the student the answer. We assist the student in solving their problems by giving them leading hints.

Suppose you have five pairs of wires. Each pair can be T (for transmit) or R (for receive). Let a sequence like TTRTR mean that the 1st pair if T, the 2nd pair is T, the 3rd pair is R, the 4th pair is T and the 5th pair is R.
How many such sequences can there be? Hint: For the 1st position we can put a T or an R, for the 2nd position we can put a T or an R, ... , for the 5th position we can put a T or an R. So for each position we can pick from two letters to put there.

Sometimes looking at smaller numbers are helpful as you can actually write out all the combinations.
 
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