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Class 10MathematicsPair of Linear Equations in Two VariablesAlgebraic methods: Substitution method and Elimination method.Hard
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What is the value of (x+y) from (0.4x+0.7y=5.3) and (0.8x-0.2y=3.8)?

Answer and explanation

Correct answer: \(x+y=\frac{161}{16}\)

Multiply both equations by 10 to remove decimals: \(4x+7y=53\) and \(8x-2y=38\). Dividing the second equation by 2 gives \(4x-y=19\), so \(y=4x-19\). Substituting this into the first equation, \(4x+7(4x-19)=53\), gives \(x=\frac{93}{16}\) and \(y=\frac{17}{4}\). Therefore, \(x+y=\frac{161}{16}\). Note that \(\frac{93}{16}\) is the value of \(x\) alone, not of the sum. Exam tip: remove decimals first when solving linear equations with decimal coefficients.

Related tags

Pair Of Linear EquationsSubstitution MethodElimination MethodDecimal CoefficientsAlgebraClass 10Algebraic Methods: Substitution Method And Elimination Method.Algebraic Methods Substitution Method And Elimination Method
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10 more MCQs
  1. 1In the equation \(2x-y=4\), what is the value of \(y\) when \(x=3\)?
  2. 2Which equation is obtained by simplifying (6x+3y=12)?
  3. 3What is the point of intersection of the lines \(4x+3y=34\) and \(4x-y=10\)?
  4. 4If the lines \(x+y=9\) and \(kx+3y=23\) both pass through the point \(\left(4,5\right)\), what is the value of \(k\)?
  5. 5While solving a pair of linear equations in two variables by the elimination method, in which situation can one variable be eliminated directly?
  6. 6What is the \(x\)-coordinate of the point of intersection of the lines \(4x+5y=31\) and \(3x-2y=1\)?
  7. 7If the two lines have a unique point of intersection (r, s) that satisfies 3r + s = 19 and r − s = 1, what is the value of r + s?
  8. 8The unique point of intersection of two lines is (r, s). If the lines are represented by 4r + s = 29 and r − s = 1, what is the value of r + s?
  9. 9What is the solution of the equations (x+y=5) and (x-y=1)?
  10. 10In the equations (2x+y=7) and (x=2), what is the value of (y)?
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