let us suppose that we have following task :
Average height of those people who are 18 years old is 69.6 inch and standard deviation is 1.4 inch, question is what is the proportion (percentage of those people who fall between 68.2 and 71 inch (height) ?
i know that if distribution is normal then 68% will be answer, but let us suppose that it is not normal distribution, then answer would be
$1-\frac{1}{k^2}$
that will fall $k$ standard deviation apart from mean, in our case $k=1$, if we substitute $k=1$, then we will get $0$, but how it could be? thanks in advance