45 pillars are standing in a line such that distance between any two consecutive pillars is same. A car travelling with uniform speed of 72 km/h takes 18 seconds to reach from 1st pole to 10th pole. What is the distance between 10th and 31st pole (in metres)?
Let distance between two consecutive pillars = $$d$$ metres
Speed of car = $$(72\times\frac{5}{18})=20$$ m/s
Using, distance = speed x time
Distance travelled by car from 1st to 10th pillar = $$9d=20\times18$$
=> $$d=20\times\frac{18}{9}=40$$ m
$$\therefore$$ Distance between 10th and 31st pillar = $$21d=21\times40=840$$ metres
=> Ans - (C)
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