Question on deflection of cathode rays in a magnetic field
1)  for individual charges Lorentz force F =q[v*B], so curl your right hand from velocity vector of positive charge towards magnetic field so that your thumb points at the force acting on the charge. Here we have considered positive charge 

2)It is better use this mnemonic to find out the direction of force to avoid confusion

Stretch the thumb, forefinger and middle finger of your right hand such that they are mutually perpendicular


fore finger denote direction of electron moving
middle finger denotes the direction of magnetic field (north to south on outside the magnet)
finally force direction can be found out using your the direction where your thumb is pointing 


The book is correct

Tip- If current is mentioned then Use your left hand, to avoid twisting your hand in weird ways! .