A2. Jakob is reading a book with 630 pages. On the first day, he read a third of the book. The sum of the numbers that marked the pages he read on the second day was 4410. How many pages does Jakob have left to finish the book? (The book starts with page number 1.)
(A) 210
(B) 211
(C) 230
(D) 390
(E) 400
A2. On read 210 pages on the first day. If he read $n$ pages on the second day, the sum of these page numbers was $211+212+213+\ldots+(210+n)=210 n+\frac{n(n+1)}{2}$. Therefore, $210 n+\frac{n(n+1)}{2}=4410$. From this, it follows that $210 n \leq 4410$ or $n \leq 20$. For $n=20$, $210 n+$ $\frac{n(n+1)}{2}=4410$, so he read 20 pages on the second day, leaving him with $630-210-20=400$ pages.