To add or subtract rational expressions with unlike denominators, first find the LCM of the denominator. The LCM of the denominators of fraction or rational expressions is also called least common denominator, or LCD. Write each expression using the LCD.
Answer:
Step-by-step explanation: Chemical signal is the type of communication which coordinates actions between neighboring cells . This ability originated in single cells organisms and was essential for the evolution of multicellular organisms because after a cell receives a message, it is transferred across the plasma membrane and changes are brought about within the cell in response to this message.
Since M and N are independent events, 
Step-by-step explanation:
Two events A and B are said to be independent when the probability of A happening does not depend on whether B has happened or not.
In other word, this condition can be rewrite as follows:

where
is the probability of A happening given that B has happened
is the probability of A happening
In this problem, we have:
- M and N are independent events: so M does not depend on whether N occurs or not
Therefore,

- Also, we know that

Therefore, it follows that

Learn more about probability:
brainly.com/question/5751004
brainly.com/question/6649771
brainly.com/question/8799684
brainly.com/question/7888686
#LearnwithBrainly