Assume that a set of test scores is normally distributed with a mean of 120 and a standard deviation of 20. Use the 68-95-99.7 rule to find the following quantities. a. The percentage of scores less than 120 is %. (Round to one decimal place as needed.) b. The percentage of scores greater than 140 is %. (Round to one decimal place as needed.) c. The percentage of scores between 80 and 140 is %. (Round to one decimal place as needed.)
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!
Assume that a set of test scores is
and a standard deviation of
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