question: There are 50 books in a small library. Half of them are written in English, and 10% in German. All others are written in Spanish. How many Spanish books are there?
answer: Half of the books are in English, which means 50 * 0.5 = <<50*0.5=25>>25 books.
  German books make up to 10%, which means there are 10/100 * 50 = <<10/100*50=5>>5 of them.
  So as a result there are 50 - 25 - 5 = <<50-25-5=20>>20 Spanish books in the library.
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