Given:
The length of the pipe is L.
The third harmonic has teh wavelength,

To find:
The type of the pipe
Step-by-step explanation:
The wavelength of the harmonics for a pipe closed at one end is,

The wavelength of the harmonics for a pipe open at both the ends is,

Here,

The given wavelength is,

which resembles the form,

Hence, the pipe is open at the other end.