Multiple choice The sum of the series 9, 5, 1,…. to 100 terms is 18900 18900 19900 None of these Reveal answer Fill a bubble to check yourself A Correct answer Explanation Arithmetic progression: a=9, d=-4, n=100. Sum = n/2 * (2a + (n-1)d) = 50 * (18 + 99 * -4) = 50 * (18 - 396) = 50 * -378 = -18900.