In a Park, N persons stand on the circumference of a circle at distinct points. Each possible pair of persons, not standing next to each other, sings a two-minute song ? one pair immediately after the other. If the total time taken for singing is 28 minutes, what is N?

One Answer on this Question

1. Total number of pairs is NC2^{N}C_2NC2​. Number of pairs standing next to each other = N. Therefore, number of pairs in question = NC2^{N}C_2NC2​ – N = 28/2 = 14. If N = 7,
   7C2​ – 7 = 21 – 7 = 14….
   N =7

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