Doppler effect: apparent frequency when the source or the observer moves towards the other

1. A.
   $n = n_0\frac{V+V_L}{V-V_S}$
2. B.
   $n = n_0\frac{V-V_L}{V+V_S}$
3. C.
   $n = n_0\frac{V-V_L}{V-V_S}$
4. D.
   $n = n_0\frac{V+V_L}{V+V_S}$

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1. A.
   $384$
2. B.
   $192$
3. C.
   $300$
4. D.
   $200$

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1. A.
   $0.5\%$
2. B.
   $0\%$
3. C.
   $20\%$
4. D.
   $5\%$

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