Find the mean for the following. Round to the nearest tenth.

Value Frequency   
  9       3          
 12       5         
 15       1          
 18       1         

must show work.

What this means is the data is this set of ten values. The
9 is listed 3 times, the 12 is listed 5 times, and the 15 and 
18 are listed just once each.  In other words, it means this:

   Value
     9
     9
     9
    12
    12
    12
    12
    12
    15
    18
   ---
10)120
  ----
    12 <--- the mean

So the 'mean', which is the ordinary average that you learned
way back in elementary school, is 12.  The frequency is
just a number to tell you how many of each value there are
in the data set so you don't have to type the same number over
and over in a column as in the above list. 

So don't do it the above way, instead do it this way.  You'll get
the same answer 12.  It's just a shortcut.  It's shorter to write it 
this way by adding to the above a column for "Value x frequency"

Value Frequency   Value x frequency
  9       3          9x3 = 27
 12       5         12x5 = 60
 15       1         15x1 = 15 
 18       1         18x1 = 18
       ----------------------
         10               120

Then you add the frequencies and that tells you how many values
are in the data set and the sum of the last column is the sum of all of
them.

And then you divide as in the first way: 

   
    12
10)120               

Either way you get the same mean 12.  But do in the second way,
for that's what you're learning.  "Frequency" just means how frequently
you find that number in the data set.

Edwin