Step 1: 4 and 5 are the Denominator.

Find the Multiple of the Denominator

Step 2: Multiple of 4 are: 4,8,12,16,20,24,28,32,....

Multiple of 5 are: 5,10,15,20,25,30,35,40,....

Find the Least Common Denominator

Step 3: $\therefore$ 20 is the LCD.

Ans: The LCD of 4 and 5 are 20.