Question 13
How many subsets of two elements can be removed from the set $$
\{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11\}
$$ so that the mean (average) of the nine remaining numbers is $6?$
\{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11\}
$$ so that the mean (average) of the nine remaining numbers is $6?$