They would become common denominators if there were a set of numbers such that a positive integer that every member of the set divided evenly was 8 or 10.
The lowest common denominator is 10
The lowest common denominator would be 10, so 1/2 would be 5/10 and 1/5 would be 2/10.
The least common denominator would be 50
A fraction with denominator 10 must have an odd numerator for otherwise its numerator and denominator would have 2 as a common factor and it would be simplified so that it would no longer have 10 as a denominator. So you are adding two odd numerators, both with 10 as the denominator. The sum of two odds is always even, so the result will be an even sum with 10 as the denominator. So in the answer, 2 is a common factor of the numerator and denominator and the answer can be simplified. If there is no other common factor, then the answer must have a denominator of 5.
The least common denominator for 9 and 10 is 90.
A common denominator, though not the least, is 80.
The lowest common denominator is 30
A common denominator is 210.
A common denominator, though not the least, is 240.
the common denominator of 10, 8, and 12 is 120.
10
A common denominator, though the least, is 240.