Converting Half-hourly data into average daily data

[TommyHayes1989]

Hi guys

I have a very very long list of variables, one is electricity output, which is measured every half hour. I need to convert this to daily, so obviously summing up and dividing by 48 (24 x half hours). I was just wondering if there is a quick drag option that will put blocks of 48 into one separate cell for me? I have attached the problem.
So for example C2:C49 is 1st Jan 2013, to get the daily average I have added up and divided by 48, which is in O2. But I can't click and drag down because I can't have Jan 1st and Jan 2nd combining, which would be O3 if I did. I can't do this manually because it would take ages. I have attached the document
What I need is O2 = daily average 1st Jan
O3 = daily average 2nd Jan...etc