80
According to http://thesaurus.maths.org/, The complement of a number is what you need to add to it to make it up to some specified total. For instance the 100s complement of 95 is 5; the 10s complement of 4 is 6.
you write 71 as LXXl and 20 as XX
In word forms, you can write it as 20 billion dollars, twenty billion dollars, $20 billion. Or you can write it as $20,000,000,000. There are at least 4 ways to write it, and probably more.
20 = twenty
.20
19/20 = 95/100 = .95.19 over 20 as a decimal is 0.95
x > 20
20 = XX
write about any 20 mathematicians
20x20
XX is 20 in Roman numerals
You could try "20 feet"!
20,020,050