LAMathematics

MP Board · Class 10 · Mathematics · Pair of Linear Equations in Two VariablesA fraction becomes $\frac{1}{3}$ when $1$ is subtracted from the numerator, and it becomes $\frac{1}{4}$ when $8$ is added to its denominator. Formulate the pair of linear equations in two variables representing this problem. Solve the linear equations step-by-step using the Substitution Method. Find the required fraction and verify your answer.

Step-by-Step Solution

Step 1: Define variables and formulate the fraction\nLet the numerator of the fraction be $= x$\nLet the denominator of the fraction be $= y$\nTherefore, the required fraction is $=\frac{x}{y}$

Step 2: Set up equations based on given conditions

Condition 1: When $1$ is subtracted from the numerator, the fraction becomes $\frac{1}{3}$. $$\frac{x - 1}{y} = \frac{1}{3}$$\nCross-multiplying: $$3(x - 1) = y$$ $$3x - 3 = y$$ $$3x - y = 3 \quad \text{--- (Equation 1)}$$

Condition 2: When $8$ is added to the denominator, the fraction becomes $\frac{1}{4}$. $$\frac{x}{y + 8} = \frac{1}{4}$$\nCross-multiplying: $$4x = y + 8$$ $$4x - y = 8 \quad \text{--- (Equation 2)}$$


Step 3: Solving by Substitution Method

\nFrom Equation (1), express $y$ in terms of $x$: $$y = 3x - 3 \quad \text{--- (Equation 3)}$$ \nSubstitute the expression for $y$ from Equation (3) into Equation (2): $$4x - (3x - 3) = 8$$ $$4x - 3x + 3 = 8$$ $$x + 3 = 8$$ $$x = 8 - 3$$ $$x = 5$$ \nNow, substitute $x = 5$ into Equation (3) to find $y$: $$y = 3(5) - 3$$ $$y = 15 - 3 = 12$$


Step 4: Write the Fraction\nThe numerator $x = 5$ and the denominator $y = 12$.\nTherefore, the required fraction is $\frac{5}{12}$.


Step 5: Verification

  1. Subtract $1$ from numerator: $\frac{5 - 1}{12} = \frac{4}{12} = \frac{1}{3}$ (Correct)
  2. Add $8$ to denominator: $\frac{5}{12 + 8} = \frac{5}{20} = \frac{1}{4}$ (Correct)
💡 Study Guide: This question tests core syllabus concepts from Pair of Linear Equations in Two Variables. For formulas, key summaries, and mock exam reference guides, read the full Pair of Linear Equations in Two Variables Revision Notes.
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