Question

N(AnB)=3 and n(AuB)=10, then find (p(A∆B))?​

Answer 1

I assume A ∆ B denotes the symmetric difference of A and B, i.e.

A ∆ B = (B - A) U (A - B)

where - denotes the set difference or relative complement, e.g.

B - A = {b ∈ B : b ∉ A}

It can be established that

A ∆ B = (A U B) - (A ∩ B)

so that

n(A ∆ B) = n(A U B) - n(A ∩ B) = 10 - 3 = 7

Not sure what you mean by p(A ∆ B), though... Probability?