A Tricky Math Question Along a road lie an odd number of stones placed at intervals of 10 metres.These stones have to be assembled around the middle stone. A person can carry only one stone  at a time. A man carried the job with one of the end stones by carrying them in  succession. In carrying all the stones he covered a distance of 3 km. Find the number of stones
Let us measure in units of $10$ meters, so he goes $300$ units.  If there are $n$ stones each side of center, he walks $n$ with the first stone, then $2(1+2+3+\dots (n-1))$ to collect all the stones on the side he started from, then $2(1+2+3+\dots n)$ to collect the ones on the other side.  $n+n(n-1)+n(n+1)=300, (2n+25)(n-12)=0, n=12$ so there are $25$ stones total.
its 301...3000meters/10 + 1(middle stone)