X={1,6,11,16,⋯}2018th term=1+2017×5=10086X={1,6,11,16,⋯,10086}
Y={9,16,23,30,⋯}2018thterm=9+2017×7=14128Y={9,16,23,⋯,14128}
X∩Y={16,51,86,⋯}
The last digit in X∩Y≤10086
∴16+35(m−1)≤10086⇒m≤288.7
As m is an integer so,
Number of terms,n(X∩Y)=288
Number of elements,
n(X∪Y)=n(X)+n(Y)−n(X∩Y) =2018+2018−288=3748