The finish times for marathon runners during a race are normally distributed with a mean of 195 minutes and a standard deviation of 25 minutes. (i) What is the probability that a runner will complete the marathon within 3hours? (ii) Calculate to the nearest minute, the time by which the first 8% runners have completed the marathon. (iii) What proportion of the runners will complete the marathon between 3 hours and 4 hours?
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!
The finish times for marathon runners during a race are
(i) What is the
(ii) Calculate to the nearest minute, the time by which the first 8% runners have completed the marathon.
(iii) What proportion of the runners will complete the marathon between 3 hours and 4 hours?
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