The problem defines the speed distribution function \(P(v)\), which represents particle count versus speed. The distribution \(P(v)\) is non-zero for speeds from 0 to \(2v_0\), and zero above \(2v_0\).
To find the number of particles with speeds between \(1.2v_0\) and \(1.8v_0\), we find the area under the curve in that range.
The area under the curve between \(1.2v_0\) and \(1.8v_0\) is 0.4 times the total number of particles, \(N\).
Thus, \(0.4N\) particles have speeds within this range.