Final answer:
Each student brought 2/3 of a dozen cookies, and there are 31 students, so multiplying 2/3 by 31 gives 20 2/3 dozens. We consider only whole dozens and get the answer as 20 dozens of cookies.
Step-by-step explanation:
On Tuesday morning, each student in Miss Savino's class brought in 2/3 of a dozen cookies to sell for a fundraiser. To find out how many dozen cookies were brought to the class by all 31 students, you multiply the fraction of a dozen per student by the total number of students:
2/3 dozen per student x 31 students = 62/3 dozens of cookies,
which simplifies to 20 2/3 dozens of cookies. Since we are looking for the number of whole dozens, we take the whole number part of this answer, which is 20 dozens. Therefore, the correct answer is 20 dozen cookies were brought to the class that day, which corresponds to option (b) 20.