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Question

If two distict non-zero real variables $x$ and $y$ are such that $(x + y)$ is proportional to $(x - y)$, then the value of $\frac{x}{y}$

The correct answer is
is a constant

Solving for the Ratio of x/y

The problem involves two distinct non-zero real variables, $x$ and $y$. We are given that $(x + y)$ is proportional to $(x - y)$. This proportionality implies the existence of a constant, let's call it $k$, such that:

  • $(x + y) = k(x - y)$

Our goal is to determine the nature of the ratio $\frac{x}{y}$.

Deriving the Constant Ratio

To find the value of $\frac{x}{y}$, we need to manipulate the given proportionality equation:

  1. Start with the proportionality equation: $x + y = k(x - y)$
  2. Distribute the constant $k$ on the right side: $x + y = kx - ky$
  3. Rearrange the terms to group $x$ terms together and $y$ terms together. Move $y$ terms to the left and $x$ terms to the right: $y + ky = kx - x$
  4. Factor out $y$ from the left side and $x$ from the right side: $y(1 + k) = x(k - 1)$
  5. To find the ratio $\frac{x}{y}$, divide both sides by $y$ (since $y \neq 0$) and by $(k - 1)$. Note that $k$ cannot be $1$, because if $k=1$, the equation becomes $y(2) = x(0)$, which implies $2y=0$, meaning $y=0$. However, $y$ is given as a non-zero variable. Therefore, $k \neq 1$, and $(k-1)$ is non-zero. $\frac{x}{y} = \frac{1 + k}{k - 1}$

Since $k$ represents a constant of proportionality, the expression $\frac{1 + k}{k - 1}$ will always yield a specific numerical value. This value does not depend on the specific values of $x$ or $y$, as long as they satisfy the initial condition. Therefore, the ratio $\frac{x}{y}$ is a constant.

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Important Questions from Ratio and Proportion

  1. If the ratio of three numbers A, B and C is 2 ∶ 3 ∶ 5, and the sum of the squares of these numbers is 3800, then the value of C is:

  2. A bag contains ₹310 in the form of 5 rupee, 2 rupee and 1 rupee coins in the ratio 4 ∶ 3 ∶ 5. What is the number of 5 rupee coins? 

  3. The ratio of three numbers is 3 ∶ 5 ∶ 4 and the sum of their squares is 11250. Find the sum of the numbers.

  4. When 'x' is subtracted from each of the numbers 22, 39, 56 and 107, then the resulting numbers, in this order, are in proportion. What is the mean proportional between (x + 3) and (3x - 7)?

  5. The salaries of Ravi and Sumit are in the ratio 4 ∶ 5. If the salary of each is increased by Rs. 6,000 the new ratio becomes 35 ∶ 40. What will be Sumit's increased salary?

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