L.et A be the set of all 50 students of class X in a school. Let f : A → N be function defined by f (x) = roll number of student x. Show that f is one-one but not onto.

A is the set of all 50 students of class X in a school.
No two different students of the class can have same roll number.
Therefore, f must be one-one.
We can assume without any loss of generality that roll numbers of students arc from 1 to 50. This implies that 51 in N is not roll number of any student of the class. so that 51 can not be image of any element of X under f. Hence, f is not onto.