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CAT-2004-Previous Years Paper

Question
12 out of 35
 

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-min song, one pair after the other. If the total time taken for singing is 28 min, what is N?



A 5
B 7

C 9
D None of the above

Ans. B

Each person will form a pair with all other persons except the two beside him. Hence, he will form (n – 3) pairs.

If we consider each person, total pairs = n(n 3) but here each pair is counted twice.

Hence, the actual number of pairs =

They will sing for × 2 = n(n3) min

Hence, n (n3) = 28

n2– 3n – 28 = 0

n = 7 or 4

Discarding the –ve value: n = 7

CAT-2004-Previous Years Paper Flashcard List

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