To find the mean of the prices of the car you would just add up your prices then divide them by the amount of number you had.
20, 15, 30, 18, 22
You would add them up = 105 than divide by 5 because you have five original numbers. So your mean = 21
To find the median just put your numbers in numerical order and then cross of the end numbers until you get to the middle number.
Like if you were given
8 19 20 6 15 put them in order 20 19 (15) 8 6
15 is your median. there are five numbers in this set, odd right?
well Sometimes though you are given a set number set that equals even
So if you had to find the median of
8 16 4 6 27 12, put them in order 27, 16, (12, 8), 6, 4
You have two middle numbers, if this happens, Add them and then always divide by 2. So the median for this set would be 10.
Sorry I can't explain the other stuff