Solve the simultaneous equations x + y = 4 and 2x + y = 7. What is the value of x?

Answer and explanation

Correct answer: A. 3

  1. Step 1: Subtract the first equation from the second: (2x + y) - (x + y) = 7 - 4, so x = 3. Step 2. Check in the first equation: y = 4 - 3 = 1, and 2(3) + 1 = 7. Answer: 3. Why not the others: 1: That is the value of y, found from x + y = 4. 4: Subtracting the two equations gives x exactly; one more does not satisfy both equations. 2: Subtracting the two equations gives x exactly; one less does not satisfy both equations.

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