Explain simply why 21 is the correct answer to: 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?. Explanation:
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.