+59 In the given pattern, find the 9th number in the 121st row.
1
2 3
6 5 4
7 8 9 10
15 14 13 12 11
16 17 ...
+128474 Notice that the final number in row N =
(N) (N+1) / 2
For instance....in Row 2 the final number is (2)(2+1) /2 = 2*3 /2 = 3
And in Row 5 is (5) (5 + 1) / 2 = 5 * 6 /2 = 30 /2 = 15
So....in Row 120, the final number should be (120)(121) /2 = 60 (121) = 7260
So....the 9th number in Row 121 should be 7260 + 9 = 7269
