The lifespan of a certain brand of bicycle tyre is normally distributed with a mean of 1200 km and a standard deviation of 80 km. (i) Find the probability that a randomly chosen tyre has a lifespan of less than 1100 km. (ii) Determine the value of c, to the nearest integer, if it is found that 4% of the tyres are not road-worthy after c km. (iii) A random sample of 10 tyres is randomly selected, find the probability that their average lifespan will be less than 1100 km.
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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