Along a road lie an odd number of stones placed at intervals of 10m. 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	Choose the correct choice from the following answers:
A) 35 B) 15 C) 29 D) 31 E) 29

Rationale: explanation : if he travels 10 m for the first stone he has to travel that dist back as well . . . so he travels 2 * 10 m dist for the first stone and so on . = > 2400 = 2 * ( 10 + 20 + 30 . . . . 10 n ) using formula for ap = > 2400 = 2 * n / 2 * ( 2 * 10 + ( n - 1 ) * 10 ) . = > 2400 = 10 n 2 + 10 n . on solving this , we get n = 15 as the positive root , so total numer of stones on both sides = 30 . and including the one which he was at = 31 . answer : d
Answer: D