If 3x + 4y = 25 and 3x + y = 13, what is the value of y?
Answer and explanation
Correct answer: y = 4
The governing concept is elimination in a pair of linear equations. The coefficient of x is 3 in both equations, so subtracting the second equation from the first removes the x-term without changing the solution. We obtain (3x + 4y) − (3x + y) = 25 − 13, which gives 3y = 12. Dividing both sides by 3 gives y = 4. Substitution confirms the result: 3x + 4(4) = 25 gives x = 3, and 3(3) + 4 = 13. Thus option C is correct. Options A, B and D do not make the two equations consistent with the same x-value.
Frequently asked questions
What is the correct answer to this question?
y = 4
Why is this the correct answer?
The governing concept is elimination in a pair of linear equations. The coefficient of x is 3 in both equations, so subtracting the second equation from the first removes the x-term without changing the solution. We obtain (3x + 4y) − (3x + y) = 25 − 13, which gives 3y = 12. Dividing both sides by 3 gives y = 4. Substitution confirms the result: 3x + 4(4) = 25 gives x = 3, and 3(3) + 4 = 13. Thus option C is correct. Options A, B and D do not make the two equations consistent with the same x-value.
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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