Vinay fires two bullets from the same place at an interval of 12 minutes but raju sitting in a train approaching the place hears the second report 11 minutes 30 seconds after the first. What is approximate speed of train if sound travels at the speed of 330 metres per second?
you are right! Thumbs up!
but how is that?
I mean the distance traveled by sound in 30 seconds = distance traveled by train in 11.5 mins, how is that?
Isn’t here anything got to do with sum of speeds of sound and train? :s
hey diana… good eve…
see the train travels towards the source of the sound… he travels for 11.5 min till he hears second sound… if the train had stood its ground then the second sound would also have been heard after 12 min… but 30 sec earlier coz train travels forward.. i think i got a sketch of a similar kind on fb.. https://www.facebook.com/ttchamp.pai.. i will forward u
thank you for posting the problem.. itz a nice 1
2 units *extra* as compared to the other option (for convenience, since the distance is 5/12, we assumed the total length as 12 units. So from one side 5 units, from the other, 7 units).
In arithmetic, it is often a good idea to compare two situations and look at the difference between them rather than looking at the whole problem. It is one of the possible ways to simplify things in your head.
CAT-holics 
Vinay fires two bullets from the same place at an interval of 12 minutes but raju sitting in a train approaching the place hears the second report 11 minutes 30 seconds after the first. What is approximate speed of train if sound travels at the speed of 330 metres per second?
diana : is the answer 14.3 m/s… coz train completes 330*30 metres in 11.5 min
you are right! Thumbs up!
but how is that?
I mean the distance traveled by sound in 30 seconds = distance traveled by train in 11.5 mins, how is that?
Isn’t here anything got to do with sum of speeds of sound and train? :s
hey diana… good eve…
see the train travels towards the source of the sound… he travels for 11.5 min till he hears second sound… if the train had stood its ground then the second sound would also have been heard after 12 min… but 30 sec earlier coz train travels forward.. i think i got a sketch of a similar kind on fb.. https://www.facebook.com/ttchamp.pai.. i will forward u
thank you for posting the problem.. itz a nice 1
Thanks Girish for the help 🙂
regards
J
Ya, thanks Girish. I need think over a bit though. 🙂
And thanks J 😉
fab method!
awesome concept.. i have seen this sum often but used to skip it. But now i want to see such problems again 🙂
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it looks like, to cycle from A to B it just takes two units for a cycle. But how. just because he is in between A & B? how?
2 units *extra* as compared to the other option (for convenience, since the distance is 5/12, we assumed the total length as 12 units. So from one side 5 units, from the other, 7 units).
In arithmetic, it is often a good idea to compare two situations and look at the difference between them rather than looking at the whole problem. It is one of the possible ways to simplify things in your head.
regards
J