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A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is ƒ 1 . If the speed of the train is reduced to 17 m/s, the frequency registered is ƒ 2 . If speed of sound is 340 m/s, then the ratio ƒ 1 /ƒ 2 is -

1. 19/18
2. 20/19
3. 21/20
4. 18/17

Correct answer: 19/18

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