Shixiong Y. answered 11/24/19
Hi, I am a PhD student in Electrical Engineering.
According to the assumption that [(19^a)^b]^c = 19^19, we can rewrite it as,
19^(abc) = 19^19
which can further be simplified to abc = 19.
Now consider that a,b and c are all positive integers, and 19 is a prime intrinsically, so the only option is that,
a*b*c = 1*1*19, i.e., a,b, and c can only equal 1, 1, and 19, respectively and in any order.
Therefore, the average of a,b and c should be (1+1+19)/3 = 7.