Question

there is a guest house on outskirts of a city. Kilometre stones are to be arranged on the road on bom
sides of the house. A man starts from the guest house G carrying 1 kilometre stone in a loading hosham a
puts it at 1 km distance and comes back. Then he drops 2nd stone at 2 km distance and comes back. He
completes the journey on both sides and leaves for home from last km stone. If the distance travelled is 210
km, find the number of stones laid.
san
NA
1 km
1 km​

Answer 1

If You look closely the series is of AP

At 1st stone he walks 2 km

At 2nd stone he walks 4 km

At 3rd stone he walks 6 km

This series will go on as 2,4,6,8...

Summation of the series is 210 (Sn)

First term (a) = 2

Common Difference (d) = 2

Use formula of Sn = n/2 [ 2a + (n-1) d ]

By substituting all the value you will get value of n to be 14

So he laid down 14 stones on road.