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Exercises Probability and the bell curve

Example 7.8 from Statistics, 7.3 Using the Central Limit Theorem

(part 4)

d. Find the 90^th percentile for the total of 75 stress scores. Draw a graph.

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Solution
d. Let k = the 90^th percentile.

Find k where P(Σx < k) = 0.90.

$k = 237.8$

Figure 7.7

The 90^th percentile for the sum of 75 scores is about 237.8. This tells us that 90 percent of all the sums of 75 scores are no more than 237.8 and 10 percent are no less than 237.8.

invNorm(0.90,(75)(3), $(\sqrt{75})$ (1.15)) = 237.8

How did it go?

Previous (part 3)Next (part 1)

From Statistics (High school edition) by OpenStax (Rice University), section 7.3, licensed under CC BY 4.0. Original at openstax.org. We split the solution into steps; the words, numbers and figures are the book's. OpenStax doesn't endorse this site.