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Balkan MO Shortlist
2008 Balkan MO Shortlist
C1
C1
Part of
2008 Balkan MO Shortlist
Problems
(1)
Professor D of some univeristy of Somewhere
Source: Balkan MO ShortList 2008 C1
4/5/2020
All
n
+
3
n+3
n
+
3
offices of University of Somewhere are numbered with numbers
0
,
1
,
2
,
…
,
0,1,2, \ldots ,
0
,
1
,
2
,
…
,
n
+
1
,
n+1,
n
+
1
,
n
+
2
n+2
n
+
2
for some
n
∈
N
n \in \mathbb{N}
n
∈
N
. One day, Professor
D
D
D
came up with a polynomial with real coefficients and power
n
n
n
. Then, on the door of every office he wrote the value of that polynomial evaluated in the number assigned to that office. On the
i
i
i
th office, for
i
i
i
∈
\in
∈
{
0
,
1
,
…
,
n
+
1
}
\{0,1, \ldots, n+1 \}
{
0
,
1
,
…
,
n
+
1
}
he wrote
2
i
2^i
2
i
and on the
(
n
+
2
)
(n+2)
(
n
+
2
)
th office he wrote
2
n
+
2
2^{n+2}
2
n
+
2
−
n
−
3
-n-3
−
n
−
3
.[*] Prove that Professor D made a calculation error [*] Assuming that Professor D made a calculation error, what is the smallest number of errors he made? Prove that in this case the errors are uniquely determined, find them and correct them.