SOLUTION: One page is missing from a book(that page has two sides,so 2 page numbers).Now the sum of the pages in that book is 8. What are the missing page numbers? Can you help me out the co

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Question 255094: One page is missing from a book(that page has two sides,so 2 page numbers).Now the sum of the pages in that book is 8. What are the missing page numbers? Can you help me out the correct method of arriving at the answer?
Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
One page is missing from a book(that page has two sides,so 2 page numbers).Now the sum of the pages in that book is 8. What are the missing page numbers? Can you help me out the correct method of arriving at the answer?

Suppose the book originally had n pages

Then the sum of the page numbers originally was %28n%28n%2B1%29%29%2F2

Suppose page number k and k+1 were torn out. So

%28n%28n%2B1%29%29%2F2-k-%28k%2B1%29=8

%28n%28n%2B1%29%29%2F2-k-k-1=8

%28n%28n%2B1%29%29%2F2-2k-1=8

%28n%5E2%2Bn%29%2F2-2k-1=8

%28n%5E2%2Bn%29%2F2-2k-9=0

Multiply both sides by 2

%28n%5E2%2Bn%29-4k-18=0

n%5E2%2Bn-4k-18=0

For that to have a rational solution,
its discriminant must be a perfect square.

Discriminant = b%5E2-4ac

1%5E2-4%281%29%28-4k-18%29

1%2B16k%2B72

16k%2B73

All perfect squares end with 1, 4, 5, 6, or 9

Therefore the number to which 73 is added,
namely 16k, in order to get a perfect square 
must end in 8, 1, 5, or 3

That number is 16k, and all multiples of 16 
end in an even digit
 
So 16k must end in 8, the smallest multiple of 16 
that ends in 8 is 48 which is 16*3

so the smallest such value is k=3

That gives the solution as page k = 3 and page k + 1 = 4

So the pages numbers remaining in the book are

pp. 1,2, and 5 and their sum is 8. It really wasn't a "book",
but was only a leaflet!

Edwin