Solve the simultaneous equations x + y = 10 and x - y = 4. What is the value of x?
Answer and explanation
Correct answer: D. x = 7, found by adding the equations to get 2x = 14
- Step 1: Add the two equations: 2x = 14, so x = 7. Step 2. Check: y = 10 - 7 = 3 and 7 - 3 = 4. Answer: x = 7. Why not the others: x = 3 is y (7 + 3 = 10 and 7 - 3 = 4); x = 6 would need y = 4 and a difference of 2; x = 14 forgets to divide by 2.
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