This article is from the Puzzles FAQ, by Chris Cole chris@questrel.questrel.com and Matthew Daly mwdaly@pobox.com with numerous contributions by others.
How many times per day do the hour and minute hands of a clock form a
right angle?
arithmetic/clock/right.angle.s
44. Twice each hour equals 48, less one between 2:00 and 4:00 and one between
8:00 and 10:00 for both A.M. and P.M.
 
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