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 work this out in a step by step way to be sure we have the right answer.
21
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.

.

Final answer: 21