Discussion

Explanation:

Let mean proportion of 4 and 9 be x.

⇒ $\frac{4}{x}=\frac{x}{9}$

∴ Mean proportional = $\sqrt{4 \times 9}$ = 2 × 3 = 6.

[Remember: Mean proportion of 2 numbers a and b is always $\sqrt{a\times b}$]

Hence, option (c).

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