I have to following table:

Date Amount Total
1-Jan-07 0:15 0:15
2-Jan-07 0:15 0:30
3-Jan-07 0:20 0:50
1-Feb-07 0:10 0:10
10-Feb-07 0:10 0:20
12-Feb-07 0:30 0:50
2-Mar-07 1:00 1:00
20-Mar-07 0:25 1:25
and so on

What formula do I use on column "C" so that it keeps a running total for
only that month (date being on column "A").

Regards
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capt