Column 1(date) Column 2 (values): how to find corresponding max/sum value based on date

Hi guys,

I have a simple table with 2 columns: left column is "date and time" and the right column is "number". I need to use a function to look at the left column and sees if they are all in 1 date then sums the corresponding numbers in the right column and put it in 3rd column. I have 4661 rows for 13/11/2012 to 23/11/2012 and finally I need to end up with just 11 rows for each date and a corresponding number (sum of all numbers for that specific date)

The problems are:
1- some days have more data than the other days.
2- the left column is a cobmination of date and time for example this is one of them: 23/11/2012 08:46:43

I've tried sumproduct but it has been unsuccessful yet :-/

appreciate it if any one can give me a hand.

Thanks,