[Excel] averaging then charting

I have some excel data where I take 5 measurements Refr. DUT Count258.76 267 500258.86 267 500258.86 268 500 258.86 267 500258.76 266 500356.64 367 510356.54 366 510356.45 365 510356.45 366 510356.54 366 510464.8 476 520464.8 476 520464.89 475 520464.8 476 520464.89 475 520I'd like to average every 5 in the Refr. and DUT columns, and then chart that results. What's the best way to do the averaging and copying the results into another sheet for charting? Number of data points is not know in advance, but it will always be divisible by 5 without remainder. TIA -- Wacky Races 2012!