Chebyshev's inequality also called as Chebyshev’s Theorem. It defines that at least 1-1/K^{2} of data from a sample must fall down within K standard deviations from the mean, where K is any positive real number larger than one.

K = Standard Deviation

Daily students study for an average time of 4 hours with standard deviation of 15 minutes. Calculate the fraction value if the students study between 3 and 5 hours?

Standard Deviation (K) = 4

The mean time is one hour. [3 to 5 hours, where the average mean is one hour]
One hour corresponds to four standard deviation (K) = 4 [60min/15min]
P(X-μ<2σ) = 1 - (1/4^{2})
P(X-μ<2σ) = 1 - (1/16)
P(X-μ<2σ) = 1 - 0.0625
P(X-μ<2σ) = 0.9375
So, Chebyshev's inequality says that at least 93.75% of the data values of any probability distribution must be within 4 standard deviations of the mean.