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What can be said about P[ 0 < X < 40 ] ?

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 ] ?

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Andre W. | Friendly tutor for ALL math and physics coursesFriendly tutor for ALL math and physics ...
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Use Chebyshev's inequality: If X is a random variable with expected value μ and  non-zero variance σ2, then for any real number k > 0, P(|X-µ|<k)≥1-σ2/k2.
With µ=20=σ2=k you get
P(|X-20|<20) ≥ 1-20/20² = .95
P(0 < X < 40) ≥ .95