Suppose that 20 pillars of the same height have been erected along the boundary

of a circular stadium. If the top of each pillar has been connected by beams with the

top of all its non-adjacent pillars, then the total number of beams is : 

  • Option 1)

    170

  • Option 2)

    180

  • Option 3)

    210

  • Option 4)

    190

 

Answers (1)

Any two non-adjacent pillars are joined by beams.

\therefore no. of beams = no. of diagonals

                          =^{20}C_2-20

                          =\frac{20\times 19}{2}-20

                          =190-20

                          =170

Option (1) is correct.


Option 1)

170

Option 2)

180

Option 3)

210

Option 4)

190

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