Say you got 68/80
all you have to do is multiply this by 100
$${\frac{{\mathtt{68}}}{{\mathtt{80}}}}{\mathtt{\,\times\,}}{\mathtt{100}} = {\mathtt{85}}$$
So you to 85% which is the same as 85/100 or 0.85
another example
23/30
$${\frac{{\mathtt{23}}}{{\mathtt{30}}}}{\mathtt{\,\times\,}}{\mathtt{100}} = {\frac{{\mathtt{230}}}{{\mathtt{3}}}} = {\mathtt{76.666\: \!666\: \!666\: \!666\: \!666\: \!7}}$$
just round this off to 77% (It is closer to 77 than it is to 76)
that is 77/100
Say you got 68/80
all you have to do is multiply this by 100
$${\frac{{\mathtt{68}}}{{\mathtt{80}}}}{\mathtt{\,\times\,}}{\mathtt{100}} = {\mathtt{85}}$$
So you to 85% which is the same as 85/100 or 0.85
another example
23/30
$${\frac{{\mathtt{23}}}{{\mathtt{30}}}}{\mathtt{\,\times\,}}{\mathtt{100}} = {\frac{{\mathtt{230}}}{{\mathtt{3}}}} = {\mathtt{76.666\: \!666\: \!666\: \!666\: \!666\: \!7}}$$
just round this off to 77% (It is closer to 77 than it is to 76)
that is 77/100