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Question

Find the mean proportional between 36 and 81.

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
54

Calculating Mean Proportional Between 36 and 81

The mean proportional (or geometric mean) between two numbers, say a and b, is a number x such that the ratio a : x is equal to the ratio x : b. Mathematically, this is represented as:

\( \frac{a}{x} = \frac{x}{b} \)

This can be rewritten as:

\( x^2 = a \times b \)

Therefore, the mean proportional x is the square root of the product of the two numbers:

\( x = \sqrt{a \times b} \)

Step-by-Step Calculation

  1. Identify the two numbers given: a = 36 and b = 81.
  2. Substitute these values into the formula for the mean proportional:

    \( x = \sqrt{36 \times 81} \)

  3. Calculate the product of the two numbers:

    \( 36 \times 81 = 2916 \)

  4. Find the square root of the product:

    \( x = \sqrt{2916} \)

    Alternatively, calculate the square root of each number first:

    \( x = \sqrt{36} \times \sqrt{81} \)

    \( x = 6 \times 9 \)

  5. The result is the mean proportional:

    \( x = 54 \)

The mean proportional between 36 and 81 is 54.

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