At the library, 50 books were checked out that day from the display. 5 copies of Sandry's Book were checked out and 15 copies of Howl's Moving Castle. If only two other books were checked out (Harry Potter and the Lightning Thief) and they were both checked out in equal quantities, how many copies of the Lightning Thief were checked out?	Answers.
A) 5 B) 10 C) 15 D) 20 E) 25
First, subtract the number of other books that were checked out from the total:   50-5-15= 
<gadget id="calculator">  50-5-15</gadget>
<output>30</output>
30. As the remaining two books were checked out in equal quantities, simply divide 30 by 2: 30/2=15. The answer is 15, 15.
<result>C</result>
At the library, 50 books were checked out that day from the display. 5 copies of Sandry's Book were checked out and 15 copies of Howl's Moving Castle. If only two other books were checked out (Harry Potter and the Lightning Thief) and they were both checked out in equal quantities, how many copies of the Lightning Thief were checked out?