Aprofessor is interested in the average length of books in her library. she has divided her books into a few different categories: 235 books on mathematics, 290 books on sports, and 166 books on interior design. rather than examining all the books, she plans to use a stratified sample of 50 books. how many of the sports books should she choose?

Step-by-step explanation:

First of all we need to find the proportion of the sample. To do that, we sum all the books and then divide by the sample we need, which is 50

, because we need 50 books among 691 total.

Now, with this ratio, which is the same for all sample we would make here, we find the stratified sample of books, specifically, for sports books which are 290.

Thefore, she should take 21 sports books.

Remember that stratified sampling refers to a type of sampling method where the population is divided into separate groups, which in this case represented the type of books. Then, we use a "probability" sample, or a proportion of the sample to apply it.

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step-by-step explanation:

in problems involving proportions, we can use cross products to test whether two ratios are equal and form a proportion. to find the cross products of a proportion, we multiply the outer terms, called the extremes, and the middle terms, called the means.

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