X is a normally distributed random variable with mean 45 and standard deviation 10. What is the probability that X is between 35 and 55? Use the 0.68−0.95−0.997 rule and write your answer as a decimal. Round to the nearest thousandth if necessary.
Q. X is a normally distributed random variable with mean 45 and standard deviation 10. What is the probability that X is between 35 and 55? Use the 0.68−0.95−0.997 rule and write your answer as a decimal. Round to the nearest thousandth if necessary.
Calculate Z-score for X=35: We got a mean (μ) of 45 and a standard deviation (σ) of 10. Let's find the z-score for X=35.Z=σX−μ=1035−45=10−10=−1.
Calculate Z-score for X=55: Now let's do the same for X=55.Z=σX−μ=1055−45=1010=1.
Find Probability for 35<x<55:< b=""> So we're looking for P(35 < X < 55), which is the same as P(\mu - \sigma < X < \mu + \sigma). According to the 0.68-95-0.997 rule, the probability that X is within one standard deviation (μ±σ) of the mean is about 0.68.
Find Probability for 35<x<55:< b=""> So we're looking for P(35 < X < 55), which is the same as P(\mu - \sigma < X < \mu + \sigma). According to the 0.68-95-0.997 rule, the probability that X is within one standard deviation (μ±σ) of the mean is about 0.68. Therefore, P(35 < X < 55) is approximately 0.68.
More problems from Find probabilities using the normal distribution I