Question

[x : x is a positive multiple of 3]

Answer 1

S={x:x is a positive multiple of 3 less than 100}

⟹S={3,6,9,12,⋯,99}

⟹n(S)=33

P={x:x is a prime number less than 20}

⟹P={2,3,5,7,11,13,17,19}

⟹n(P)=8

n(S)+n(P)=33+8=41