The figure below shows the network connecting cities, A, B, C, D, E and F. The arrows indicate permissible direction of travel. What is the number of distinct paths from A to F?

9

10

11

None of these

Correct Answer : A

The sum of 3rd and 15^{th} elements of an arithmetic progression is equal to the sum of 6th, 11th and 13^{th} elements of the same progression. Then which element of the series should necessarily be equal to zero?

855,7695,69255,623295,_____

123, 211,299,156,244,____