document.write( "Question 721761: There are between 50 and 100 books on a shelf. Exactly 20% of them are textbooks. Exactly 1/7 of them are novels. How many books are on the shelf? \n" ); document.write( "

Algebra.Com's Answer #442494 by josgarithmetic(39630) $\"\"$ $\"About$

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This relies on the search for whole numbers such that 20% gives a whole number and 1/7 gives a whole number. 70 fits this. You can look in the multiples of 7, and choose from the ones between 50 and 100. This is more effective than setting up equations $\"0.20%28t%2Bn%29=t\"$ and $\"%281%2F7%29%28t%2Bn%29=n\"$ and use of $\"50%3C=t%2Bn%3C=100\"$ . \n" ); document.write( "

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