If a, b, c, d are 4 positive numbers, show that
Have you heard of the AM-GM inequality?
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
Have you left out some constraint on this problem?
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.