Standardize a normal interval, calculate probabilities and determine a lower quantile.

Standardize a normal interval, calculate probabilities and determine a lower quantile.

10 marks
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Reaction times of human beings are normally distributed with a mean of 0.76 seconds and a standard deviation of 0.06 seconds.

  1. The graph below is that of the standard normal curve. The shaded area represents the probability that the reaction time of a person chosen at random is between 0.70 and 0.79 seconds.[6]
    1. Write down the value of a and of b.
    2. Calculate the probability that the reaction time of a person chosen at random is (a) greater than 0.70 seconds and (b) between 0.70 and 0.79 seconds.
  2. Three percent (3%) of the population have a reaction time less than \(c\) seconds.[4]
    1. Represent this information on a diagram similar to the one above. Indicate clearly the area representing 3%.
    2. Find c.

Solution:

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Answer:For the lowest 3%, \(c=0.76+0.06z_{0.03}=0.647\) seconds.

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