Dear genious
You always has the answer
But,please tell us the method
It's because you only ask for the answer, and I am not that good(clear) at explaining.
**Edit** another reason is to give others a chance to figure it out...for all they know I could be wrong
It's just algebra, more or less.
Let X = a page number
Therefore X + 1 = the next consecutive page, x+2, the page after that X+n = the last page and n+1 = total number of pages
If two pages were missing the equation would be
x + (x+1) = 9808
2x + 1 = 9808
2x = 9807
x = 4903.5 which obviously is wrong since you can't be missing half a page( well you can, but you know what I mean)
3 pages would be
x + (x+1) + (x+2) = 9808
3x+3= 9808
4 would be
x + (x+1) + (x+2) + (x+3) = 9808
4x+6
see the pattern of the second nomial? It's a simple arithmetic sequence:
F(n) = Sum (0...N)
and how it relates to the coefficient of the first?
So a general formula can be create thus:
nX + F(n-1) = 9808
nX = 9808 - F(n-1)
X = (9808-F(n-1)) / n
n = number of pages
X = begining page
I used trial and error to get the correct n, (did it in an excel spreadsheet)