If X and Y are two sets such that n(X)=17, n(Y)=23 and n(X∪Y)=38, find n(X∩Y)

It is given that:
n(X)=17, n(Y)=23, n(X∪Y)=38
n(X∩Y)=?
Using the formula
n(X∪Y) = n(X) + n(Y) - n(X∩Y)
∴ 38 = 17 + 23 - n(X∩Y)
⇒ n(X∩Y) = 40 - 38 = 2
∴ n(X∩Y) = 2