arithmetic
posted by Marty (F) .
Please complete the following sequence so that, after the first two terms, each successive term is the average of all the preceeding terms. 20__ __ 28 __ __

If the sequence is 20 x y 28 ... then
y = (20+x)/2 = 10 + x/2
28 = (20+x+y)/3 = (20+x+10+x/2)/3 = 10+x/2
18 = x/2
x=36
y=28
20 36 28 28 28 28