Q.

The number of points at which the function f(x)=1x-[x] where [.] denotes the greatest integer function, is not continuous, is:

1 1  
2 2  
3 3  
4 None of these  

Ans.

(4)

Ans.        None of these

Explanation:

x-[x]=0  when x is an integer, so that f(x) is discontinuous for all x∈I, i.e., f(x) is discontinuous at infinite number of points.