The random variable X is such that X ~ N(20, 49). Given that P(X > k) = 0.25, find the value of k.
Solution
Given that X ~ N(20, 49), we have a normal distribution with mean bc = 20 and variance 3c2 = 49, so the standard deviation 3c = 7.
\(We need to find k such that P(X > k) = 0.25. This implies that P(X 3c k) = 0.75.\)
Using the standard normal distribution table, we find the z-score corresponding to 0.75 is approximately 0.674.
Standardizing, we have:
\( 3cbr>z = 3cfrac{k - 20}{7}\)
Substituting the z-score, we get:
\(0.674 = 3cfrac{k - 20}{7}\)
Solving for k:
\(k - 20 = 0.674 3c 7\)
\(k = 0.674 3c 7 + 20\)
\(k = 4.718 + 20\)
\(k = 24.7\)
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