The reduced mass of the muonic hydrogen atom is given by:
$\mu = \frac{m_{\mu} m_{p}}{m_{\mu} + m_{p}} \approx \frac{207 m_{e} m_{p}}{207 m_{e} + m_{p}}$
Since $m_{p} \gg m_{e}$, we can approximate the reduced mass as:
$\mu \approx \frac{207 m_{e} m_{p}}{m_{p}}
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