How do you convert a score to a decimal over 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