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avatar+63 

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 ... 

 Feb 24, 2019
 #1
avatar+103120 
+2

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

 

 

cool cool cool

 Feb 24, 2019
 #2
avatar+63 
+1

Thanks!

Dominator416  Feb 24, 2019

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