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Problem
Problem
If
(
18
r
−
2
)
+
2
(
18
r
−
1
)
+
(
18
r
)
≥
(
20
13
)
\binom{18}{r-2} + 2\binom{18}{r-1} + \binom{18}{r} \ge \binom{20}{13}
(
r
−
2
18
)
+
2
(
r
−
1
18
)
+
(
r
18
)
≥
(
13
20
)
, then the number of values of
r
r
r
are
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