Question

3. To hear a distinct echo, the minimum distance of a reflecting surface should be
(a) 7 m
(b) 17 m
(c) 27 m
(d) 10 m
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Answer 1

$\LARGE{ \underline{\underline{ \bf{Required \: answer:}}}}$

To hear a distinct echo, the minimum distance of a reflecting surface should be:

10 m