Books on a Bookshelf
Number Theory
Level
1
There are several books on a bookshelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?
The answer is 9.
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1 solution
Since the book is 4th from the left, there must be 3 books on its left. For the same reason, there must be 5 on its right. The number of books on the shelf must be the number of books on its left+the number of books on its right+1 (itself)=9