Question

Which is the least common denominator of 3/4 4/5 and 2/3

Answer 1

Wow!  Here you have 3 fractions with 3 different denominators that have nothing in common.  In cases such as this one you find the LCD by mult. all of the given denominators together.  Thus, in this case, your LCD is 4(5)(3) = 60.

Answer 2

To find the least common denominator of the three fractions, list out the multiples of each denominator:

Multiples of 3: {3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60}
Multiples of 4: {4,8,12,16,20,24,28,32,36,40,44,50,55,60}
Multiples of 5: {5,10,15,20,25,30,35,40,45,50,55,60}

The least common denominator of these three fractions is 60.