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.
A) 35
B) 15
C) 29
D) 31
E) 29
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.   =&gt; 2400 = 2 * (10 + 20 + 30 .... 10n) using formula for AP   =&gt; 2400 = 2 * n/2*(2*10 + (n-1)*10) .   =&gt; 2400 = 10n2 + 10n .   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 : 31
<result>D</result>
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