Question 18

A bus starts running with some initial speed and its speed increases every hour by 9 km/hr. If it takes 11 hours to cover a distance of 572 km, then what was the initial speed (in km/hr) of the bus?

Solution

Let initial speed of bus = $$x$$ km/hr = Distance travelled in 1st hour

Speed after 1 hour = $$(x+9)$$ km/hr = Distance travelled in 2nd hour and so on.

Similarly, distance travelled in 11th hour = $$(x+90)$$ km

Total distance (using sum of an arithmetic series) = $$\frac{11}{2}[(x)+(x+90)]=572$$

=> $$x+45=\frac{572}{11}=52$$

=> $$x=52-45=7$$

$$\therefore$$ Initial speed of bus = 7 km/hr

=> Ans - (B)

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