It helps to simplify the sums and differences when done adding and subtracting.
LCM is only used for whole numbers.
If it's like this: "There are 4 books in a bag and two of the four are fiction. Jess randomly pulls one out of the bag and replaces it. What is the probability of getting two fiction books?" Then you...
The least common denominator (LCD) is the least common multiple (LCM) of the denominators.
When the numerator and denominator have another common factor besides ' 1 '.