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Nov 2013 p63 q2
3150
A factory produces flower pots. The base diameters have a normal distribution with mean 14 cm and standard deviation 0.52 cm. Find the probability that the base diameters of exactly 8 out of 10 randomly chosen flower pots are between 13.6 cm and 14.8 cm.
Solution
First, we find the probability that a single flower pot has a base diameter between 13.6 cm and 14.8 cm. We standardize the values using the normal distribution:
\(P(13.6 < X < 14.8) = P\left( \frac{13.6 - 14}{0.52} < z < \frac{14.8 - 14}{0.52} \right)\)
\(= P(-0.7692 < z < 1.538)\)
Using the standard normal distribution table, we find:
\(= \Phi(1.538) - [1 - \Phi(0.7692)]\)
\(= 0.9380 - [1 - 0.7791]\)
\(= 0.7171\)
Now, we use the binomial distribution to find the probability that exactly 8 out of 10 flower pots have diameters in this range: