Given the set A={2,3,4,5,6}.
The relation R is defined on A×A such that (x,y)R(z,w) if and only if x divides z and y≤w.
The number of elements in R is the number of ordered pairs ((x,y),(z,w)) satisfying these conditions. Since the conditions for (x,z) and (y,w) are independent, the total number of elements in R will be the product of the number of pairs (x,z) satisfying x divides z and the number of pairs (y,w) satisfying y≤w.
First, we find the number of pairs (x,z)∈A×A such that x divides z:
For x=2, z∈{2,4,6} (3 pairs)
For x=3, z∈{3,6} (2 pairs)
For x=4, z∈{4} (1 pair)
For x=5, z∈{5} (1 pair)
For x=6, z∈{6} (1 pair)
Total number of pairs (x,z)=3+2+1+1+1=8.
Next, we find the number of pairs (y,w)∈A×A such that y≤w:
For y=2, w∈{2,3,4,5,6} (5 pairs)
For y=3, w∈{3,4,5,6} (4 pairs)
For y=4, w∈{4,5,6} (3 pairs)
For y=5, w∈{5,6} (2 pairs)
For y=6, w∈{6} (1 pair)
Total number of pairs (y,w)=5+4+3+2+1=15.
The total number of elements in the relation R is the product of the number of these pairs:
Total elements = 8×15=120.
Answer: 120