SOLUTION: 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?

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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?
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
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.