11n>10n+9n ⇒11n−9n>10n ⇒(10+1)n−(10−1)n>10n nC010n+nC110n−1+nC210n−2+....} −{C0nC010n−nC110n−1} ⇒2(nC110n−1+nC310n−3)>10n For, n=1⇒2.1×10 For, n=2⇒2(2)×100 For, n=3⇒2(3⋅102+1)×1000 For, n=5⇒ 2(5C110n+5C3102+5C5)×105 Hence, n∈{5,6,7,......100} ∴ Number of elements =96