A standing man, observes rain falling with velocity of 20 m/s at an angle of 37º with the vertical. The man then moves with constant horizontal velocity and observes the rain to fall at an angle 45° with the vertical . Then the speed of man can be :

 $V_m\pm 20\sin 37°=20\cos 37°$ or  $V_m=4or28m/s$

The above values are velocities of man are two extremes one in the direction of horizontal component of rain and the other being in the opposite direction of horizontal component of rain. 
So it is possible to observe rain falling at an angle 45° with vertical by the man if his speed lies between 4 m/s and 28 m/s (both included).