To add fractions, we have to convert them to a common denominator. Since $${\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{2}} = {\mathtt{12}}$$, we can convert 5/6 to a denominator of 12 by multiplying it by 2/2: $${\frac{\left({\mathtt{5}}{\mathtt{\,\times\,}}{\mathtt{2}}\right)}{\left({\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{2}}\right)}}$$ = $${\frac{{\mathtt{10}}}{{\mathtt{12}}}}$$. Then we add $${\frac{{\mathtt{5}}}{{\mathtt{12}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{10}}}{{\mathtt{12}}}}$$ = $${\frac{{\mathtt{15}}}{{\mathtt{12}}}}$$, which simplifies down to $${\frac{{\mathtt{5}}}{{\mathtt{4}}}}$$, and then can be converted to the fraction $${\mathtt{1}}$$$${\frac{{\mathtt{1}}}{{\mathtt{4}}}}$$ or 1.25.
To add fractions, we have to convert them to a common denominator. Since $${\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{2}} = {\mathtt{12}}$$, we can convert 5/6 to a denominator of 12 by multiplying it by 2/2: $${\frac{\left({\mathtt{5}}{\mathtt{\,\times\,}}{\mathtt{2}}\right)}{\left({\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{2}}\right)}}$$ = $${\frac{{\mathtt{10}}}{{\mathtt{12}}}}$$. Then we add $${\frac{{\mathtt{5}}}{{\mathtt{12}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{10}}}{{\mathtt{12}}}}$$ = $${\frac{{\mathtt{15}}}{{\mathtt{12}}}}$$, which simplifies down to $${\frac{{\mathtt{5}}}{{\mathtt{4}}}}$$, and then can be converted to the fraction $${\mathtt{1}}$$$${\frac{{\mathtt{1}}}{{\mathtt{4}}}}$$ or 1.25.