SOLUTION: You read 10 pages in a book, stopping at the top of page x. On what page did you begin?

Here are two ways to get the answer:

First way:

Since you stopped at the top of page x, you did not read page x.

We look at a sequence of numbers:

If x=11, she read pages 1,2,3,4,5,6,7,8,9,10, she began at page 1, 
and since x=11, and she started on page 1, and 1 is 11-10, then
that means she started on page x-10.

If x=12, she read pages 2,3,4,5,6,7,8,9,10,11 she began at page 2, 
and since x=12, and she started on page 2, and 2 is 12-10, then
that means she started on page x-10.

If x=13, she read pages 3,4,5,6,7,8,9,10,11,12 she began at page 3, 
and since x=13, and she started on page 3, and 3 is 13-10, then
that means she started on page x-10.

We can keep going with this as far as we like, but we see that she
started on page x-10 every time.

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Second way:

Another way to look at it is that if you ended at the top of page x, 
you did not read page x, and the last page you read was page x-1. 
So the 10 pages you read, from the last page to the first page, were:

 1. x-1
 2. x-2
 3. x-3
 4. x-4
 5. x-5
 6. x-6
 7. x-7
 8. x-8
 9. x-9
10. x-10

So the first page you read was page x-10.

Edwin