Any multiple of their lowest common multiple (which is 180), namely:
180, 360, 540, 720, 900, 1080, 1260, 1440, 1620, 1800, 1980, 2160, 2340, 2520, 2700, 2880, 3060, 3240, 3420, 3600, 3780, 3960, 4140, 4320, 4500, 4680, 4860, 5040, 5220, 5400, 5580, 5760, 5940, 6120, 6300, 6480, 6660, 6840, 7020, 7200, 7380, 7560, 7740, 7920, 8100, 8280, 8460, 8640, 8820, 9000, 9180, 9360, 9540, 9720, 9900, 10080, 10260, 10440, 10620, 10800, 10980, 11160, 11340, 11520, 11700, 11880, 12060, 12240, 12420, 12600, 12780, 12960, 13140, 13320, 13500, 13680, 13860, 14040, 14220, 14400, 14580, 14760, 14940, 15120, 15300, 15480, 15660, 15840, 16020, 16200, 16380, 16560, 16740, 16920, 17100, 17280, 17460, 17640, 17820, 18000, ...
LCD(18, 4, 20) = 180
A common denominator of 20 and 30 is 600. This is NOT the least common denominator, though.
If those are all denominators, the LCD is 360.
A common denominator is 72.
The lowest common multiple, or lowest common denominator, of 18 and 28 is 252.
A common denominator, though not the least one, is 12*20 = 240.
A common denominator, though the least, is 260.
A common denominator, though not the least, is 5616.
The answer is 20
20
18
The common denominator of any two or more whole numbers, such as 10 12 18 and 20, will always be one (1) because 'common denominator' refers to the denominators of two or more fractions or mixed numbers, not whole numbers. So, a set of whole numbers (x,x) would have to be converted to their fraction equivalents, i.e., x/1, which will always yield a denominator of 1.