Average speed when equal distances x are covered at speeds v1 and v2

1. A.
   $\frac{2v_{1}v_{2}}{v_{1} + v_{2}}$
2. B.
   $\frac{2x}{v_{1} + v_{2}}$
3. C.
   $\frac{v_{1}v_{2}}{2\left( v_{1} + v_{2} \right)}$
4. D.
   $\frac{v_{1} + v_{2}}{2}$

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1. A.
   $v = v_{1} + v_{2}$
2. B.
   $v = \frac{v_{1} + v_{2}}{2}$
3. C.
   $\frac{2}{v} = \frac{1}{v_{1}} + \frac{1}{v_{2}}$
4. D.
   $\frac{1}{v} = \frac{1}{v_{1}} + \frac{1}{v_{2}}$

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