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Starter. The length of leaves on a tree are normally distributed with a mean of 14cm and a standard deviation of 4cm. Find the probability that a leaf is: Longer than 14cm Between 14cm and 17cm in length Between 12cm and 15cm in length.

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  1. Starter • The length of leaves on a tree are normally distributed with a mean of 14cm and a standard deviation of 4cm. • Find the probability that a leaf is: • Longer than 14cm • Between 14cm and 17cm in length • Between 12cm and 15cm in length

  2. Find the number of leaves in a sample of one hundred leaves which would be expected to be less than 9cm in length. Two leaves are randomly selected. What is the probability that both are less than 9cm?

  3. Note 10: Inverse Normal • Sometimes we know the probability and are asked to find the cut-off point that gives that probability. • Method to solve: • Draw a bell shaped curve • Use the inverse normal function on the calculator

  4. Example 1: The length of Christmas tree branches from a plantation are normally distributed with a mean of 180cm and a standard deviation of 20cm. 5% of all branches are considered too small to use as Christmas tree decorations. Find the maximum length of branches that are too small.

  5. 0.05 X 180 Calculator – Inverse Normal New Calculator – Tail Left Area = 0.05 Std dev = 20 Mean = 180 X = 147.1 Maximum length of branches that are too small is 147.1cm

  6. Example:The heights ofall year 12 pupils were measured and found to be normally distributed with a mean of 170cm and a standard deviation of 7cm. Find the height that 75% of the students are taller than. 0.75 X 170

  7. 0.75 X 170 X = 165.3 75% of students are taller than 165.3cm New Calculator Tail Right Area = 0.75 Std dev = 7 Mean = 170 Old Calculator Area to left = 0.25 Std dev = 7 Mean = 170

  8. Exercises : NuLake Page 31 - 34

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