Nancy can hula hoop for 10 minutes. Casey can hula hoop 3 minutes less than Nancy. Morgan can hula hoop three times as long as Casey. How long can Morgan hula hoop? Let's be accurate as possible.
Casey can hula hoop 3 minutes less than Nancy so she can hula hoop for 10 - 3 = 7 minutes. Morgan can hula hoop three times as long as Casey, who can hula hoop for 7 minutes, so she can hula hoop for 3 * 7 = 21 minutes.
The answer: 21.