Q.Find the fundamental, first overtone and second overtone frequencies of a pipe, open at both the ends, of length 25 cm if the speed of sound in air is 330 m/s.

[!TLDR] Open pipe: $n=v/2L=330/0.5=660$ Hz; first overtone $=2n=1320$ Hz; second overtone $=3n=19 …

For a pipe open at both ends of length $L=25$ cm $=0.25$ m with $v=330$ m/s: the fundamental frequency is $n=\dfrac{v}{2L}=\dfrac{330}{2\times0.25}=\dfrac{330}{0.5}=660$ Hz. Since an open pipe supports ALL harmonics (Long Answer 9), the first overtone is the second harmonic, $2n=2\ti …

Compute the open-pipe fundamental via $n=v/2L$, then multiply by 2 and 3 for the first and second overtones respect …

Using the closed-pipe overtone sequence (3n, 5n for the first/second overtone) instead of the open-pipe sequence (2n, 3 …