The response time of a system, X, is a random variable with a mean of 20 seconds and a
variance of 20 seconds. What can be said about P[ 0 < X < 40 ] ?
Use Chebyshev's inequality: If X is a random variable with expected value μ and non-zero variance σ^{2}, then for any real number k > 0, P(|X-µ|<k)≥1-σ^{2}/k^{2}.