Find the sum of all integers between 100 and 1000 that are divisible by 9.
Answer: A
The numbers are 108, 117, ..., 999. This is an A.P. with \(a=108, d=9, a_n=999\). Number of terms: \(999=108+(n-1)9 \Rightarrow 891=(n-1)9 \Rightarrow n-1=99 \Rightarrow n=100\). Sum = \(\frac{100}{2}(108+999) = 50(1107) = 55350\).