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20 Dec 2025, 08:58
Kudos
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Answer Choice: C
Since the time of passing each other (30s) is a weighted average of the individual passing times (40s and 25s), the ratio of speed is inversely proportional to their distances from 30. Thus (40-30) : (30-25) = 2:1 so the ratio of slower to faster speed is 1:2 (since higher speed contributes less time).
Since the time of passing each other (30s) is a weighted average of the individual passing times (40s and 25s), the ratio of speed is inversely proportional to their distances from 30. Thus (40-30) : (30-25) = 2:1 so the ratio of slower to faster speed is 1:2 (since higher speed contributes less time).
20 Dec 2025, 08:59
Kudos
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Let Speed of train 1 = v1
Speed of train 2 = v2
Length of train 1 = L1
Length of train 2 = L2
When train 1 passes the person: Time = L1/v1 = 40 =>L1 = 40v1
when train 2 passess: Time = L2/v2 => L2 = 25v2
Also we are given when the two trains pass each other in opposite directions
Time=L1+L2/v1+v2, which is equal to 30 seconds
=> 40v1+25v2/v1+v2 = 30
=> 40v1+25v2=30v1+30v2
=> 10v1=5v2
=> v2=2v1
Hence v1:v2 = 1:2 Answer (c)
Speed of train 2 = v2
Length of train 1 = L1
Length of train 2 = L2
When train 1 passes the person: Time = L1/v1 = 40 =>L1 = 40v1
when train 2 passess: Time = L2/v2 => L2 = 25v2
Also we are given when the two trains pass each other in opposite directions
Time=L1+L2/v1+v2, which is equal to 30 seconds
=> 40v1+25v2/v1+v2 = 30
=> 40v1+25v2=30v1+30v2
=> 10v1=5v2
=> v2=2v1
Hence v1:v2 = 1:2 Answer (c)
20 Dec 2025, 18:04
Kudos
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Once I realized that this was a weighted averages problem in disguise as a rate/time/distance problem, I was able to solve it relatively quickly. If it's asking for the ratio or weight of the faster and slower train, we can figure that out with the teeter totter method.
Basically for 25 and 40, the distance of each of those from 30, in this case the weighted average, is 5 and 10. This means that the ratio of the faster train to the slower train is 10:5, or 2:1. So the slower train to faster train is 1:2.
Basically for 25 and 40, the distance of each of those from 30, in this case the weighted average, is 5 and 10. This means that the ratio of the faster train to the slower train is 10:5, or 2:1. So the slower train to faster train is 1:2.
