Write out the prime factorizations of the denominators:  and  .
In
this case, the denominators have no factors in common. (Which makes it a
pretty sure bet they're going to hook up.) In this case, the LCD is
merely the product of the two denominators: 510. That's a pretty big
denominator, but we'll have to live with it. We should at least ask it
to start paying rent. | 
and 
.
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