How can high pitch sound travel less faster? I read these three sentences
Frequency is inversely proportional to wavelength
Frequency increase causes an increase in pitch.
They mean high frequency has small wavelength.
So they travel less farther.
In that case, i should to hear a whistle sound less (high-pitch).
But it is more audible right.
Please help me understand the reason
 A: I think you're mixing two different concepts:

*

*velocity of the transmission: different velocity of transmission of signals with difference frequency is related to dispersion;

*length of transmission: the reduction of intensity of the signal depends on the "shape" of the signal (e.g. amplitude of spherical waves in a non-diffusive medium goes with $1/r$, for plane waves is approximately constant), and on the diffusion (or attenuation).

Dispersion. The speed of sound in air is approximately the same over a wide range of frequency (and amplitude) of the signal, i.e. air behaves as a non-dispersive medium. Sound signals have velocity of transmission equal to $c$, where
$c^2(\rho_0,s_0) = \left(\dfrac{\partial P}{\partial \rho}\right)_s(\rho_0,s_0)$
Diffusion. Sound attenuation can be described by Stokes' law, examining the effects of the volume viscosity on plane waves, see https://en.wikipedia.org/wiki/Stokes%27s_law_of_sound_attenuation. To cut a long story short, air behaves as a low-pass filter, attenuating the signals with higher frequency (like many other systems in nature, far from their natural frequencies - resonance).
Anyway, it's likely that the main effect is the "directionality" of the sound wave, i.e. if the sound propagates as a spherical signal, or a plane wave. Have you ever tried that pairs of parabolic mirrors where you whisper something in a focus of one mirror and someone else clearly listen to your whisper in the focus of the other paraboloid?
