1. 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?
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By: anil on 05 May 2019 02.27 am
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) = $$frac{11}{2}[(x)+(x+90)]=572$$ => $$x+45=frac{572}{11}=52$$ => $$x=52-45=7$$ $$ herefore$$ Initial speed of bus = 7 km/hr => Ans - (B)
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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) = $$frac{11}{2}[(x)+(x+90)]=572$$ => $$x+45=frac{572}{11}=52$$ => $$x=52-45=7$$ $$ herefore$$ Initial speed of bus = 7 km/hr => Ans - (B)