One number is the square root of the other. Looked at the other way, the other number is the square of the first.
4^2 = 16 and 4 + 16 = 20; x=16^2=256 , so the 4th root is 4 and the square root is 16.
But the title asks us to think twice. The only thing I can think of would be if x^(1/4) were negative and x^(1/2) were positive. I guess it could be the other way around, if you make different choices, so that x^(1/2) is not (x^(1/4))^2, but rather (x^(1/4))^2.
If x^(1/4) = 5 and x^(1/2) = 25 then the sum is 20; one of the 4th roots of 625 is 5 and one of the square roots is 25. So both these choices we get 25 +(5) = 20.
Edited on September 12, 2016, 10:34 am

Posted by Charlie
on 20160912 10:33:10 