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?

To determine how long it will be before Sally has to take all three quizzes in one day again, we need to find the least common multiple (LCM) of the two quiz intervals: the weekly spelling quiz and the history quiz every third Monday.

The spelling quiz happens every Monday, which is a 7-day interval.
The history quiz happens every third Monday, which is a 21-day interval.

To find the LCM of 7 and 21, we can list the multiples of each number until we find a common multiple:

Multiples of 7: 7, 14, 21, 28, ...
Multiples of 21: 21, 42, ...

We see that the first common multiple is 21. Therefore, Sally will have to take both quizzes on the same day again in 21 days.

Note: In this context, we assume that the quizzes always follow the same weekly pattern without any changes.