Question

Given $A=\{2,3,4\},B=\{2,5,6,7\}.$ Construct an example of the following:

A mapping which is not injective from A to B.

• A. $\{(2,5),(3,5),(3,7)\}.$
• B. $\{(2,5),(3,5),(4,7)\}.$
• C. $\{(2,5),(3,6),(4,7)\}.$
• D. None of these

Answer 1

The correct option is B $\{(2,5),(3,5),(4,7)\}.$

Given $A=\{2,3,4\},B=\{2,5,6,7\}.$
Option A is not a mapping as element 3 of set A has 2 image .
Option B, is not an injective mapping as images of distinct elements 2 and 5 are not distinct.
Option C is an injective map as distinct elements has distinct images.