Notice that "cast ballots" and "voted in the election" mean the same thing. I.e.:

60.5% of the voting age voters cast ballots

85.7% of registered voters cast ballots

OK, let

a = # of people voting age

r = # of registered voters

v = # of people who voted

So we can rewrite the first two statements:

0.605 a = v

0.857 r = v

Notice this means:

0.857 r = 0.605 a

Now we want to find r/a (portion of voting age people who were registered), so we can rearrange the equation to say:

r/a = 0.605 / 0.857

and put that into your calculator to get your answer. (And multiply by 100 to get a percentage, if you want). I suggest you Percentage calculator through this you get more results about How to calculate percentage .