\( X \) is a normally distributed random variable with mean 41 and standard deviation 7 . What is the probability that \( X \) is between 55 and 62 ? Use the \( 0.68-0.95-0.997 \) rule and write your answer as a decimal. Round to the nearest thousandth if necessary.
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To solve this problem using the \( 0.68-0.95-0.997 \) rule, we start by finding the Z-scores for the values 55 and 62 using the formula: \[ Z = \frac{(X - \mu)}{\sigma} \] where \( \mu = 41 \) and \( \sigma = 7 \). For \( X = 55 \): \[ Z_{55} = \frac{(55 - 41)}{7} = \frac{14}{7} = 2 \] For \( X = 62 \): \[ Z_{62} = \frac{(62 - 41)}{7} = \frac{21}{7} = 3 \] Now, we need to find the probability that \( X \) lies between \( Z_{55} = 2 \) and \( Z_{62} = 3 \). According to the empirical rule, approximately 95% of values lie within 2 standard deviations of the mean (which is between \( Z = -2 \) and \( Z = 2 \)), and about 99.7% lies within 3 standard deviations. The area to the left of \( Z = 2 \) (where \( P(Z < 2) \)) is about 0.9772, and the area to the left of \( Z = 3 \) (where \( P(Z < 3) \)) is approximately 0.9987. Now we calculate: \[ P(2 < Z < 3) = P(Z < 3) - P(Z < 2) = 0.9987 - 0.9772 = 0.0215 \] Thus, the probability that \( X \) is between 55 and 62 is approximately \( 0.022 \) when rounded to the nearest thousandth.