Which expression is the lcd of these fractions 4/x^2y 20/xy

LCD of      4       and   20
             (x^2)y           xy

Without any mathematical operations involved, ask yourself how many common variables are in the denominators.   x^2 is the same as (x)(x)

so we have           4              and             20      
                        (x)(x)(y)                          (x)(y)

So what we have in common is one (x) and one (y).

The LCD is xy
    

Bis the right answer