Answer: The best measure of central tendency for these data is the Median.
Explanation:
The median divides a set of numbers into two equal halves, this means that it measures the centre of a given set of numbers arranged in an orderly manner from the lowest to the highest.
If it is an odd set of arranged numbers, then the median is the middle value. If however it consists of an even set of arranged numbers, then the average of the two numbers in the middle of the set is the median.
When data is assymetrical, skewed, or unbalanced as we have in this case where the researcher has a missing score, then the median is a better measure of central tendency than others like the mean and mode because in such cases, it gives a more accurate representation of the middle of the data set.
Therefore, if the researcher chooses to record a time of zero for the student that failed to solve the problem, it will not affect the median value. Also, if the researcher chooses to work without the time of the student who did not solve the problem, then he adopts a sample size of n = 14. Again this will not significantly affect the calculation of the median as an average of the two numbers in the middle of the data set will have to be computed.