Question

Let A = {x : x ϵ N, x is a multiple of 3} and B = {x : x ϵ N and x is a multiple of 5}. Write A ∩ B.

Answer 1

Here, 

A = {X:XϵN,X is a multiple of 3} and 

B = {X:XϵN,X is a multiple of 5}. 

A⋂B = {X:XϵN,X is a multiple of 3} and{X:XϵN,X is a multiple of 5} 

= {X:XϵN,X is a multiple of 3 and 5} 

= {X:XϵN,X is a multiple of 3*5 = 15} 

= {X:XϵN,X is a multiple of 15}