9709/63 Mathematics May Jun 2011 Online Test | Cambridge AS and A Level MCQ
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The weights of letters posted by a certain business are normally distributed with mean $20{\text{ }}g$. It is found that the weights of 94% of the letters are within $12{\text{ }}g$ of the mean.
a) Find the standard deviation of the weights of the letters.
b) Find the probability that a randomly chosen letter weighs more than $13{\text{ }}g$.
c) Find the probability that at least 2 of a random sample of 7 letters have weights which…