The average amount parents spent per child on back-to-school items in August 201

Question

The average amount parents spent per child on back-to-school items in August 2012 was $656 with a standard deviation of $225.Assume the amount spent on back-to-school items is normally distributed.

11. The probability is 0.91 that the amount spent on a randomly selected child is no less than what value?

12. The probability is 0.36 that the amount spent on a randomly selected child will be between what two values equidistant from the mean? Find the lower and upper endpoints.

13. The probability is 0.84 that the amount spent on a randomly selected child is at most what value?

Explanation / Answer

11)for top 91 percent will lie at 9th percentile for which z =-1.3408

therefore corresponding value =mean +z*std deviation =354.33

12) for middle 36 percent lies between 32 and 68 percentile for which z =-/+0.4677

therefore corresponding value =mean -/+z*std deviation =550.77 to 761.23

13)

for 84th percentile z =0.9945

therefore corresponding value =mean +z*std deviation =879.75

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