For the given data set, the data values are listed in ascending order, where , , , and are constants. The mean of the data set is , and the range is . The mean of and is greater than the mean of and .
Which choice gives the value of ?
For data-set questions with several unknown values, avoid trying to find every unknown separately. First use the overall mean to find a total or subtotal. Next, convert statements about means of groups into equations involving group sums. Finally, use the range, which connects the smallest and largest values, to isolate an endpoint.
Hints
Find the missing subtotal
Use the mean and the number of data values to find the total of all values. Then subtract the sum of the five known values.
Group the unknown values
Let one sum represent and another represent . Translate the statement about the two pair means into a relationship between those sums.
Connect the endpoints
Once you know , use the range . Adding those two equations isolates the larger endpoint.
Desmos Guide
Use algebra as the primary method
Algebra is faster here because the problem gives relationships among sums of values. Desmos can verify the two group sums.
Graph the group-sum equations
Let represent and let represent . Enter and . Click their intersection; its -coordinate is the endpoint sum .
Verify the larger endpoint
In a new expression line, enter . This combines the endpoint sum with the range to calculate the larger endpoint.
Step-by-step Explanation
Find the total of the unknown values
Because there are data values and their mean is , their total is .
The five known values have total
Therefore,
Use sums for the two pairs
Let and . Then
The mean of and is greater than the mean of and , so
Thus . Combining this with gives
Use the range
Since the values are in ascending order, the range is . Add this equation to :
Therefore,