General form of A.P is a, a + d, a + 2d, a + 3d….. Here a9 = 40; so 9th term is a + 8d = 40 then S17 =? ⇒ Sn = (n/2) [2 x a + (n – 1)d] = 0 ⇒ S17 = (17/2) [2a + 16d] ⇒ (17) [a + 8d] ⇒ 17 x 40 = 680
120, 139, 196, 291, 420, 595
13, 24, 69, 272, 1355, 8248
115, 138, 163, 190, 220, 250
384, 1152, 144, 432, 56, 162
48, 112, 144, 192, 310, 732
169, 217, 193, 239, 217, 265
11 9 20 18 37 36
...72, 36, 54, 135, 470.5, 2126.25
6, 22, 76, 314, 1580, 9600
2592 1300 656 331 169.5 88.75
...
