If you need to know the number of days
in a month, count your knuckles. Using
your left hand, start at your pinky with
January and name the months as you tap
each knuckle- including the grooves in
between. Months that land on a knuckle
have 31 days, and months that fall in the
grooves have 30 or fewer days. Once you
reach July, skip the thumbs and continue
to your right hand, or start over with
August on the pinky of your left. SourceSource 2