math
posted by kelvin .
Mrs. Cason gives her class a spelling quiz every Monday,and a history quiz every third Monday . Sally smarty is in Mrs. Carson's class. She received a grade of 100% on all three quizzes today. How long will it be before she again has to take all three quizzes in on day?

I see spelling quiz(every Monday) and history quiz(every third Monday).
But I do not see a third quiz. Am I missing something?