$A=\left\{x\in \mathbb{N}:x\mid 60\text{i}x\text{nie jest liczbą pierwszą}\right\}=\left\{1,4,6,10,12,15,20,30,60\right\}$   

$B=\left\{x\in \mathbb{N}:x=2k+1\text{dla}k\in \mathbb{N}\right\}=\left\{1,3,5,7,9,11,\dots \right\}$  

$C=\left\{x\in \mathbb{N}:x\ge 20\right\}=\left\{20,21,22,23,\dots \right\}$  

Wyznaczamy zbiory B' i C'.

$B{}^{\prime }=\left\{2,4,6,8,10,12,\dots \right\}$  

$C{}^{\prime }=\left\{0,1,2,3,4,\dots ,18,19\right\}$  

Zatem:

$A\cap B{}^{\prime }\cap C{}^{\prime }=\left\{4,6,10,12\right\}$