What should be added to

Let $x$ be added.

$\therefore x+\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{5}\right)=3$

$\Rightarrow x+\left(\frac{15}{30}+\frac{10}{30}+\frac{6}{30}\right)=3$

$\Rightarrow x+\left(\frac{15+10+6}{30}\right)=3$

$\Rightarrow x+\frac{31}{30}=3$

$\Rightarrow x=\frac{3}{1}-\frac{31}{30}$

$\Rightarrow x=\frac{90}{30}-\frac{31}{30}$

$\Rightarrow x=\frac{90-31}{30}$

$\Rightarrow x=\frac{59}{30}$