Final answer:
To find the missing data value when the average of 8 data values is -7, calculate the total sum of all values and subtract the sum of the given values from this total to find the missing number. The correct option is C.
Step-by-step explanation:
The student has asked for help in finding the missing data value given that the average of 8 data values is -7. To find the missing value, we need to use the formula for the average, which is the sum of all values divided by the number of values.
Since the average is -7 for 8 values, the sum of all values will be -7 times 8, which equals -56. If we add up all the given data values and subtract from -56, we will find the missing value.
Let's suppose the sum of the 7 given numbers is 'S'. Therefore, the missing value 'M' can be found using this equation: S + M = -56. By solving for 'M', we can determine which option is correct.