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Combinatorics

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Difficult

Pair Sums to 7

COMBIN-NLQYSU

Let:

$$X=\{ 1,2,3,4,5,6\}$$

What is the smallest number $n$ such that if $n$ integers are chosen from $X$, then at least one pair of integers is guaranteed to have sum $7$.

A

$3$

B

$4$

C

$5$

D

$6$