Probabilities question

  • Thread starter cdux
  • Start date
  • #1
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That's not exactly coursework (it's studying) but I've spammed the probabilities forum too much.

Can someone explain this part?

Knowing that P(k)=P(X=k)=c(101-k)

For a 'turtle' that can live up to 100 years, find 'c'.

And it goes

K2Vwoxp.png


I don't understand the jump from cΣk to c100(100+1)/2
 

Answers and Replies

  • #2
DrClaude
Mentor
7,601
3,997
$$
\sum_{k=1}^n k = (1+n) \frac{n}{2}
$$
To see how to get the formula, list the numbers of the sum, then sum the first with the last, the second with the second to last, etc.
 
  • #3
188
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then sum the first with the last, the second with the second to last, etc.
Ah, hacky. I was expecting a more straightforward way.

Thank you!
 

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