If 3x + 2y = 28 and mx - 2y = 12 have solution x = 5, what is the value of m?
Answer and explanation
Correct answer: 5
A stated solution must satisfy each equation simultaneously. Insert x = 5 into the first equation: 3(5) + 2y = 28, so 15 + 2y = 28 and 2y = 13. Hence y = 13/2. Substitute x = 5 and y = 13/2 into the second equation: 5m - 2(13/2) = 12, so 5m - 13 = 12. Therefore 5m = 25 and m = 5. Option C is correct. The distractors 3, 4, and 6 would produce second-equation values of 2, 7, and 17 respectively after the known y is used, not 12.
Frequently asked questions
What is the correct answer to this question?
5
Why is this the correct answer?
A stated solution must satisfy each equation simultaneously. Insert x = 5 into the first equation: 3(5) + 2y = 28, so 15 + 2y = 28 and 2y = 13. Hence y = 13/2. Substitute x = 5 and y = 13/2 into the second equation: 5m - 2(13/2) = 12, so 5m - 13 = 12. Therefore 5m = 25 and m = 5. Option C is correct. The distractors 3, 4, and 6 would produce second-equation values of 2, 7, and 17 respectively after the known y is used, not 12.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Pair of Linear Equations in Two Variables. Topic: Algebraic methods: Substitution method and Elimination method..
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