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The distance from BB to CC is thrice that from AA to BB. Two trains travel from AA to CC via BB. The speed of train 22 is double that of train 11 while traveling from AA to BB and their speeds are interchanged while traveling from BB to CC. The ratio of the time taken by train 11 to that taken by train 22 in travelling from AA to CC is

Solution

✅ Correct Option: 3
RouteTrain 1 SpeedTrain 2 Speed
A → Bss2s2s
B → C2s2sss

Time = Distance ÷ Speed

From A to B:

Train 1: Time = ds\frac{d}{s}

Train 2: Time = d2s\frac{d}{2s}

From B to C:

Train 1: Time = 3d2s\frac{3d}{2s}

Train 2: Time = 3ds\frac{3d}{s}


Train 1 total time:

ds+3d2s\dfrac{d}{s} + \dfrac{3d}{2s}

=2d2s+3d2s= \dfrac{2d}{2s} + \dfrac{3d}{2s}

=5d2s= \dfrac{5d}{2s}

Train 2 total time:

d2s+3ds\dfrac{d}{2s} + \dfrac{3d}{s}

=d2s+6d2s= \dfrac{d}{2s} + \dfrac{6d}{2s}

=7d2s= \dfrac{7d}{2s}


Notice that both total times have the same denominator (2s) and the same distance factors. This means we can directls compare the numerators:

Train 1: 5d2s\frac{5d}{2s}

Train 2: 7d2s\frac{7d}{2s}

Since the denominators are identical, the ratio is simpls 5:75:7.

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