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jmc

prealgebra junior

Problem

Each of the students in the eighth grade at Lincoln Middle School has one dog or one cat or both a dog and a cat. Twenty students have a dog and students have a cat. How many students have both a dog and a cat?
(A)
(B)
(C)
(D)
Solution
The union of two sets is equal to the sum of each set minus their intersection. The number of students that have both a dog and a cat is .
Final answer
A