5. High school textbooks don't last forever. The lifespan of all high school textbooks is approximately normal with a mean of 9 years and a standard deviation of 2.5 years. (a) What percentage of books last longer than 10 years? (b) What percentage of books last less than 5 years? (c) How old is a textbook if it lasts as no longer than 30% of all other books?

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5. High school textbooks don't last forever.
The lifespan of all high school textbooks is
approximately normal with a mean of 9 years
and a standard deviation of 2.5 years.
(a) What percentage of books last longer
than 10 years?
(b) What percentage of books last less than 5
years?
(c) How old is a textbook if it lasts as no
longer than 30% of all other books?
(d) What percentage of books last between 7
years and 12 years?
(e) If you were told that a particular book
lasted 15 years, would you be surprised?
Why? Give statistical justification for your
answer.
Transcribed Image Text:5. High school textbooks don't last forever. The lifespan of all high school textbooks is approximately normal with a mean of 9 years and a standard deviation of 2.5 years. (a) What percentage of books last longer than 10 years? (b) What percentage of books last less than 5 years? (c) How old is a textbook if it lasts as no longer than 30% of all other books? (d) What percentage of books last between 7 years and 12 years? (e) If you were told that a particular book lasted 15 years, would you be surprised? Why? Give statistical justification for your answer.
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