Answer:
d is answer i 100% sure for first
Answer: you just sech in google what is bla bla bla (don't do that ) XD
Step-by-step explanation:
<h2>
Answer:</h2>
The probability is:

<h2>
Step-by-step explanation:</h2>
It is given that:
An urn contains balls numbered 1 through 20.
A ball is chosen, returned to the urn, and a second ball is chosen.
This means that this is a case of a replacement.
Hence, one of the event is independent of the other.
Now we know that the probability to get a particular number of ball is:

( Since, there are total 20 balls and a ball of one particular number is just unique )
i.e. 
Hence, the probability that the first and second balls will be a 8 is:

Sometime you have to convert medicine amounts or maybe how much you have to cut something in surgery that you have to convert you also might use percentages figuring out the percent of something to go in a specific medication