Let the random variables X1 and X2 denote the length and width, respectively, of a manufactured part. Assume Xi is normally distributed with a mean of 2 centimeters and a standard deviation of 0.2 centimeters. Also, assume X2 is normally distributed with a mean of 4 centimeters and a standard deviation of 0.3 centimeters. Finally, assume X1 and X2 are independent. We are interested in the perimeter of the manufactured part P, which can be expressed by the equation 3. P = 2X1+ 2X2 (a) Find the mean and standard deviation of the random variable P. Find the probability that the perimeter P is between 11.8 and 12.5 (b) centimeters.
Continuous Probability Distributions
Probability distributions are of two types, which are continuous probability distributions and discrete probability distributions. A continuous probability distribution contains an infinite number of values. For example, if time is infinite: you could count from 0 to a trillion seconds, billion seconds, so on indefinitely. A discrete probability distribution consists of only a countable set of possible values.
Normal Distribution
Suppose we had to design a bathroom weighing scale, how would we decide what should be the range of the weighing machine? Would we take the highest recorded human weight in history and use that as the upper limit for our weighing scale? This may not be a great idea as the sensitivity of the scale would get reduced if the range is too large. At the same time, if we keep the upper limit too low, it may not be usable for a large percentage of the population!
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