$41$ forks are so arranged that each produces $5$ beats per sec when sounded with its near fork. If the frequency of last fork is double the frequency of first fork, then the frequencies of the first and last fork are respectively
A$200, 400$
B$205, 410$
C$195, 390$
D$100, 200$
Medium
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A$200, 400$
a (a) $n_{First} = n_{First} + (N -1)x$
$2n = n + (41 -1) × 5$
$\Rightarrow$ $n_{First} = 200 Hz$ and $n_{Last} = 400 Hz$
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