The LCD of 5 and 4 is 20.
20
60
LCD(40, 50) = 200
The LCD, or Lowest Common Denominator, is the smallest multiple of each of the denominators of a set of fractions. So, assuming that 2, 4 and 5 are denominators of fractions (1/2, 1/4 and 1/5, for example), the LCD would be 20, because 20 is the lowest number that 2, 4 and 5 multiply into. So, your new fractions would be 10/20, 5/20 and 4/20. The purpose of finding the LCD is to allow for multiplying fractions together, or simply comparing them easily.
The LCD of 5 and 4 is 20.
LCD(25, 20, 4) = 100.
Lcd of 5,4,2 is 20 because 5*4=20 and 2*10=20
20
20
20
Since 5x + 20 is a multiple of x + 4, it is automatically the LCD of this problem.
20
60
LCD(4, 5) = 20.
LCD(18, 4, 20) = 180
LCD(40, 50) = 200