ThePortForum.com

Maybe this explain why I still have those old green tiles in my kitchen

Derek

My parents both died at 53. My paternal grandfather at 51 and his father at 49.

With that genetic disposition, I wont be drinking £35,000 worth of Port, do you think you all have a responsibilty to get the good stuff out when I'm about?

Us butterflys, (thats colourful, dramatic, eye-catching, but brief), have to make the most of life.

Alan

(∑n)²/∑(n²) ≈ 10.66 as of a fraction of an hour ago.

Pardon? What does n represent to give a result of 10.66? And is that exactly 10.66 or are you pointing out that the fonts available on the board do not permit the recurring symbol to be shown?

jdaw1 wrote:Imagine a bulletin board with 4 members, whose number of posts are 1000, 1000, 1000 and 1. How many members does this bulletin board have? Well, really, in an activity-weighted sense, 3.

Mathematically the natural way to capture this is (∑n)²/(∑n²), that is, the square of the sum divided by the sum of the square: 1000+1000+1000+1 = 3001; 1000²+1000²+1000²+1² = 3000001; so (∑)²/(∑²) = 3001×3001÷3000001 ≈ 3.002.

And in an activity-weighted sense, has ≈10.66 (not recurring) members.

Another example: ten members have posted, 88, 53, 33, 20, 12, 7, 4, 3, 2, 1 times, so ∑n=223 and ∑n²=12265. Thus the activity-weighted number of members = (∑n)²/(∑n²) = 223×223÷12265 = 223÷55 ≈ 4.0545454. Now go back and look at the data: an answer of about 4 doesn’t look obviously wrong.