A set of numbers {10, 21, 17, 12, x} has the property that the mean is equal to the median.
What could the value of x be?
If x itself is to be the mean and median, then it must be the mean of the other four numbers: (10+21+17+12)/4 = 15.
If, however, the second lowest number, 12, is to be made the mean and median by making x less than that value, then (x+10+17+21)/4 = 12, or x+48 = 48, or x = 0.
Finally, if the second highest number, 17, is to be made the mean and median by making x larger than that value, then (x+10+12+21)/4 = 17, or x+43 = 68, or x = 25.

Posted by Charlie
on 20070420 11:16:22 