Answers

2015-08-05T21:31:38+08:00
18 is the second arithmetic mean  :) and the complete arithmetic mean will be 11, 18, 25, 32, 39. 
Add 7 to the arithmetic mean, 11 to find the second arithmetic mean and to find the third, add 7 to the second arithmetic mean and do it again to until you reach the fifth arithmetic mean, 39.
2 4 2
why 18? its 25
You have to find the common difference first and after that, add the common difference to the first arithmetic mean and do it again to the second arithmetic mean and do it again until you reach to the last arithmetic mean :)