A block of mass 5 kg is placed on a horizontal surface with coefficient of friction $\mu$ = 0.2, then the maximum and minimum value of force F for which the block remains at rest are (g = 10 $m/s^2$) 

If it has to move right, frictional force 0.2 x 5 x 10 = 10 N acts towards left  then maximum F value should be 25 N

if it has to move towards left, frictional force acts towards right. Net force 15 -10 = 5 N has to be applied towards right.