How did you get the answer of . from the question 20 pages in 30 min

Well, the first important step is to give some attention to understanding
what the question is.  In this case, the question probably had something
to do with finding a "unit rate".  That means how many pages in each minute.

To find the number of "pages per minute", just divide the (number of pages)
by the (number of minutes).

(20 pages) / (30 minutes) = (20/30) = (2/3) page per minute .

If you'd rather have that answer in the form of a decimal instead of a fraction,
then you could either take a pencil and divide 2 by 3 to get the decimal, or
else take your calculator and punch in  ' 2 '  ' ÷ '  ' 3 '  ' = ' .  Either way, you
find that the decimal equivalent of 2/3 is 0.666... .  The 6s keep going forever
and never end.

20/30 pages per minute.

20/30 reduces to 2/3.

2/3 = .666 which is approx .67