## Thinking Mathematically (6th Edition)

RECALL: (1) $A = B$ if and only if the elements of A and B are exactly the same. (2) Sets $A$ and $B$ are equivalent if they have the same number of elements. When written in roster method, the set on the left is $\left\{a, b, c, d, e\right\}$. This set has 5 elements. The set on the right also has 5 elements. The two sets have the same number of elements but the elements themselves are different. Thus, the two sets are equivalent.