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According to Chebyshev's rule, for any quantitative data set and any real number $k$greater than or equal to $1$, at least $1-\frac{1}{k^2}$of the observations lie within $k$standard deviations to either side of the mean, that is, $\stackrel{铃�}{x}-ks$and $\stackrel{铃�}{x}+ks$.

By Chebyshev's rule,

At least$1-\frac{1}{{(1.25)}^2}=1-\frac{1}{1.5625}=\frac{0.5625}{1.5625}=36\%$ of the observations lie within $1.25$ standard deviations to either side of the mean.

We have been given that $k=3.5$.

We need to find the percentage of observations in any data set that lie within four standard deviations to either side of the mean.

According to Chebyshev's rule, for any quantitative data set and any real number $k$greater than or equal to $1$, at least $1-\frac{1}{k^2}$of the observations lie within $k$standard deviations to either side of the mean, that is, $\stackrel{铃�}{x}-ks$and $\stackrel{铃�}{x}+ks$.

By Chebyshev's rule,

At least$1-\frac{1}{{(3.5)}^2}=1-\frac{1}{12.25}=\frac{11.25}{12.25}=91.836\%$of the observations lie within $3.5$standard deviations to either side of the mean.