5. (5 points) Xiaoming added the page numbers of a book starting from 1, and when he added them all up, he got 4979. Later, he found out that the book was missing one sheet (two consecutive page numbers). So, the book originally had $\qquad$ pages.

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5. (5 points) Xiaoming added the page numbers of a book starting from 1, and the sum he got was 4979. Later, he found that the book was missing one sheet (two consecutive page numbers). Therefore, the book originally had $\qquad$ pages.

【Solution】Solution: Let the page numbers of the book be the natural numbers from 1 to $n$. The correct sum should be
$1+2+\cdots+n=\frac{1}{2} n(n+1)$,
According to the problem, $\frac{1}{2} n(n+1)>4979$,
By estimation, when $n=100, \frac{1}{2} n(n+1)=\frac{1}{2} \times 100 \times 101=5050$,
So the book has 100 pages.
Answer: The book has a total of 100 pages.
Therefore, the answer is: 100.