Along a road lie an odd number of stones placed at intervals of 10 m. These stones have to be assembled…
The correct choice is: “31” Let there be n stones on each side of the middle stone, so 2n + 1 stones in all. The stone at distance 10i m from the middle requires a round…
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Along a road lie an odd number of stones placed at intervals of 10 m. These stones have to be assembled around the middle stone. A person can carry only one stone at a time. A man carried out the job starting with the stone in the middle, carrying stones in succession, thereby covering a distance of 4.8 km. Then, the number of stones is:
Answer and explanation
Correct answer C
The correct choice is: “31”
Let there be n stones on each side of the middle stone, so 2n + 1 stones in all. The stone at distance 10i m from the middle requires a round trip of 2 × 10i = 20i m.
One side: 20(1 + 2 + … + n) = 10n(n + 1). Both sides: 20n(n + 1) metres.
20n(n + 1) = 4800 ⇒ n(n + 1) = 240 = 15 × 16 ⇒ n = 15.
Number of stones = 2 × 15 + 1 = 31.
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