A fraction is a division.
17/5 = 3.4
3 3/4 = 3.75
19/20 = 0.95
19/20 < 17/5 < 3 3/4
19/20 is less than 3 3/4
3 3/4 is greater than 17/5
and 20 is the common denominator of the 3 fractions because 20/5 = 4, 20/4 = 5,
and 20/20 = 1
20 is a number which can be divided exactly by all the denominators.