What is the sum of the two digit multiples of 11?
What is the sum of the two digit multiples of 11?
\(S = \frac{1}{2}n(a + l)\)
\(a = 11\)
\(l = 99\)
\(n = 9\)
\(S = \frac{1}{2}9(11 + 99)\)
\(S = \frac{1}{2}9(110)\)
\(S = \frac{990}{2}\)
\(S = 495\)