Two trains start from the same point simultaneously and in the same direction. The first train travels at 40 km /h, and the speed of the second train is 25% more than the speed of first train. Thirty minutes later, a third train starts from same point and in the same direction. It over takes the second train 90 minutes later than it overtook the first train. What is the speed of the third train?
A. 20 km/h
B. 40 km/h
C. 60 km/h
D. 50 km/h
E. 80 km/h
Answer: Option C
Solution(By Examveda Team)
A _______ B ________ C Let both the trains start from point A. At point B third train overtook the first train. To overtake the first train by third train, Third train needs to cover, Distance covered by first train in $$1\frac{1}{2}$$ h = distance covered by third train in 1 h. [as third train has started 30 minutes later] In this situation distance is constant, then from, s × t = d; we get, S α $$\frac{1}{{\text{t}}}$$ Now,$$\eqalign{ & \frac{{{\text{t}} + \frac{1}{2}}}{{\text{t}}} = \frac{{\text{s}}}{{40}} \cr & \frac{{2{\text{t}} + 1}}{{\text{t}}} = \frac{{\text{s}}}{{40}}\,.\,.\,.\,.\,.\,.\,.\,.\left( 1 \right) \cr} $$ From equation (1), It is clear that time is in the ratio 3 : 2 then speed will be in 2 : 3 ratios. Hence, Speed of the Third train will be 60 km/h.
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Related Questions on Speed Time and Distance
A. 48 min.
B. 60 min.
C. 42 min.
D. 62 min.
E. 66 min.
A. 262.4 km
B. 260 km
C. 283.33 km
D. 275 km
E. None of these
A. 4 hours
B. 4 hours 30 min.
C. 4 hours 45 min.
D. 5 hours
Here,
Speed 1 and Speed 2=40 and 50kmph
In 30m F1 goes=40*1/2=20km
F2 goes=50*1/2= 25km
Let,Speed 3 =x
ATQ,
25/(x-50)-20/x-40=90/60
On solving x=60
1st train speed=40km/hr
2nd train speed=40*125/100=50km/hr
as 3rd train inter after 30 minutes
as a result, 1st train cover distance=40*1/2=20km/hr
2nd train also cover distance=50*1/2=25km/hr
let ,3rd train speed=x km/hr
so atq, 40/20-x-50/25-x=90/60
x=60km/hr.....(ans)
How did you know that it will overtake first train in one hour???