ข้อสอบคณิต O-NET - 2558

$$\begin{gathered} \mathrm{จากโจทย์} \mathrm{เนื่องจากไม่มีคอมพลีเมนต์} \\ \mathrm{กำหนดแค่ภายในวง} A, B, C \\ \mathrm{ดังรูป} \end{gathered}$$

$$\begin{gathered} \mathrm{จะได้} A = \left\{1, 2, 4, 5\right\} \\ B = \left\{2, 3, 5, 6\right\} \\ C = \left\{4, 5, 6, 7\right\} \end{gathered}$$

$$\begin{gathered} 1. \left(A\cap B\right)-C \\ = \left\{2, 5\right\}-\left\{4, 5, 6, 7\right\} \\ = \left\{2\right\} \end{gathered}$$

$$\begin{gathered} 2. A\cap \left(B-C\right) \\ = \left\{1, 2, 4, 5\right\}\cap \left\{2, 5\right\} \\ = \left\{2\right\} \end{gathered}$$

$$\begin{gathered} 3. A\cap \left(B\cup C\right)-C \\ = \left\{1, 2, 4, 5\right\}\cap \left\{2, 3, 4, 5, 6, 7\right\}-\left\{4, 5, 6, 7\right\} \\ = \left\{2, 4, 5\right\}-\left\{4, 5, 6, 7\right\} \\ = \left\{2\right\} \end{gathered}$$

$$\begin{gathered} 4. \left(A\cap B\right)-\left(B\cap C\right) \\ = \left\{2, 5\right\}-\left\{5, 6\right\} \\ = \left\{2\right\} \end{gathered}$$

$$\begin{gathered} 5. B\cap \left(A\cup C\right)-\left(A\cap B\cap C\right) \\ = \left\{2, 3, 5, 6\right\}\cap \left\{1, 2, 4, 5, 6, 7\right\}-\left\{5\right\} \\ = \left\{2, 5, 6\right\}-\left\{5\right\} \\ = \left\{2, 6\right\} \\ \mathrm{ดังนั้น} \mathrm{ตอบข้อ} 5 \end{gathered}$$