Stuart McLachlan
stuart at lexacorp.com.pg
Tue Jan 24 19:13:26 CST 2006
On 24 Jan 2006 at 16:50, Francisco Tapia wrote: > can someone answer me this: > C1 C2 > C3 1566 1770 > 0.884746 5130 5340 > 0.960674 1320 1800 > 0.733333 6440 7280 > 0.884615 1770 1800 > 0.983333 > > > > 16226 17990 > 0.901946 > If I take C1 / C2 I get C3... there must be a mathimaticall reason as to why > I can't just average column C3 to get the 90%, instead I end up with 88.93% > The larger a number, the more weight it needs to carry in the "averaging" A clearer example to show why you can't just average averages to get an overall average. Individual Averages: 1/1000 = .001 99999/1000 = 99.999 Overall average (weighted): 100000/1000 = 100 Average(?) average: (.001 + 99.999)/2 = 50 The second "average" gives equal weight to the 1 occurence in the first calculation and the 999 occurences in the second calculation. -- Stuart