Let A = (1, 2, 3} and B = {4}
How many relations can be defined from A to B.
The number of relations from set A to set B = 
n(A) = Number of elements in set A
n(B) = Number of elements in set B
Here,
n(A) = 3
n(B) = 1
Total number of relations = 
= 8
1