Question 404116
75 = 150 - 3*25 = 75, and 225 = 150 + 3*25 .  

Hence k = 3 in Chebyshev's theorem (or, within 3 sd's from the mean, plus-minus).

==> {{{P(abs (X - mu) <= 3sigma) >= 1 - 1/3^2 = 8/9}}}.

That is AT LEAST {{{88&8/9}}}% of the distribution between 75 and 225.