Add every number together and divide by the total number of numbers in the set (9) to get the following.

The mean is the average of a set of numbers. The mean is found by adding up all of the numbers in the set and then dividing by the size of the set. There are numbers in the set. The sum of number is . The mean is  divided by  which is .

Solving this question involves understanding how the equation for mean of a data set works. Let's look at the data set so far:

Since all the elements of this data set are the same (test scores), let's call the missing values t.

We know we want our final average to be an 80, so let's look at the basic equation for finding mean, with 80 in place of x:

At this point, simple algebra takes over:

 Multiply both sides by 5.

 Subtract known values from the right side and simplify.

 Simplify.

Thus, James must score an average of 70.5 on each of his remaining tests to average an 80 for the semester. This could mean he scores a 70 and 71, or a 90 and a 51, or any combination of scores that averages to at least 70.5. (By the looks of it, James is in good shape!)

To find the average cost of gifts, we simply sum all of our data points, then divide by the total number of points. In this case, we have an  of 5, so we'll have 5 numbers to play with and we'll be dividing by 5 at some point.

Some people will want to rearrange the numbers from least to greatest, but this is not strictly necessary for calculating the mean.

So on average, Annie will need to save  this year.

To find the mean, or average, of a set of data simply find the sum of all of the data and divide the total by the amount of data pieces (n), 

.

So for this set of data, 

.

11 is our average. (note that unlike finding the median and mode, the mean is not necessarily a piece of data currently in the data set)

To find the mean of the data set, all of the data values must be added together.

In this set provided, 

.

The next step is to divide the sum of the data values by the amount of data values, .

Since the answer to this is a repeating decimal, leaving it in the form of a fraction would suffice. Remember, fractions can be read as division problems, thus division problems can be written as fractions.

So  is equivalent to . 

The mean is defined as the average of the group of data.

Using the data set provided, to find the mean all we must do is add up the data and divide by the amont of data values, 

, 

n = amt of data values, x = data value.

Now that we have the formula we just plug in the numbers,

.  

To find the mean, or the average, all that is required is to add up the values and then divide by the number of data pieces in then. In this data set, we have only four pieces of data. Our equation should look like this: 

.

Once the values our added, our fraction can be simplified to: 

.

This is our mean. 

This problem is meant to divert our attention to the large numbers present. Finding the mode of a data set requires no calculation. The mode is simply the number that appears the most often.

In this set, each number appears only once, except for the number  

That, therefore, is the mode.

But this question is asking if the mode = x, and the mode is .

Then 

In order to find the mean or average number of slices of pizza eaten, we need to find the total number of slices eaten and divide it by the number of students.

Add the slices of pizza eaten by each student.

Then you divide by the number of students in the group.

The average number of slices eaten was.