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The lowest common denominator of 30 and 42 is 210.
The common denominator of any two or more whole numbers, such as 210 385 and 400, 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.
A common denominator is 210.
210
30
210
210
210
210
LCD(70, 105) = 210.
LCD(30, 35) = 210
400