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The weights of books in a bookcase are normally distributed with a mean of 11.6 pounds and a standard deviation of 1.3 pounds. There are 136 books on the bookshelf.

 

How many of the books will weigh 10 pounds or more?

 

A. 109

B. 116

C. 121

D. 130

 Apr 10, 2019
 #1
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10 pounds is BELOW the mean     11.6 - 10 = 1.6     1.6/1.3 = 1.231 standard deviations below the mean

Look at your negative z -score table 1.23  corresponds to the fraction .1093

  ....this is how many books weigh LESS than 10 pounds....the remainder   (1-.1093) will weigh MORE than 10 pounds

 

(1-.1093)(136) = ~~ 121 books weigh more than 10#

 

 

 

(Thanx CHris for spotting my typo!)

 Apr 10, 2019
edited by ElectricPavlov  Apr 10, 2019

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