**Elementary School Number Sense Lesson 14: Sets--Union**

This lesson will cover finding the

**union**of two or more sets. It is related to

**SetsIntersect**, and appeared

**4 times**this year, with a median placement at

**question # 54**.

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The union of two sets is the list of all unique elements that appear in either (or both) sets. It is denoted by the symbol

**U**. So, if:

set B = {0, 1, 2, 3, 4}, then

**A U**

**B = {0, 1, 2, 3, 4, 9, 16}**

**Example 1: {M, A, T, H}**

**U {S, M, A, R, T} has ___ elements**

- The union contains {M, A, T, H, S, R}--
*we don’t count M, A, or T twice.* - The answer is
**6**

**Example 2: {T, E, X, A, S}**

**U {T, E, C, H} has ___ elements**

- The union contains {T, E, X, A, S, C, H}
- The answer is
**7**

**Example 3: If A = {p, a, d, r, e} and B = {i, s, l, a, n, d} then the number of elements in A**

**U B is ___**

- The union contains {p, a, d, r, e, i, s, l, n}
- The answer is
**9**

**Example 4: If A = {d, a, l, l, a, s} and B = {s, t, a, r, s} then the number of elements in A**

**U B is ___**

- The union contains {d, a, l, s, t, r}--
*we don’t count a, l, or s twice.* - The answer is
**6**

**Example 5: Find the number of elements in A**

**U B if A = {t, m, s, c, a} and B = {s, t, e, m}**

- The union contains {t, m, s, c, a, e}
- The answer is
**6**

**Example 6: {F, I, R, E}**

**U {C, R, A, C, K, E, R} has ___ elements**

- The union contains {F, I, R, E, C, A, K}
- The answer is
**7**

**Up Next for Elementary School: AddSubWhole**