A company has invested $$900,000$ in a diversified portfolio and is considering investing $$100,000$ in a risk$-$free state bond with a $0\mathrm{.}42\%$ monthly yield. The financial director of the company presents the following information:

Expected Monthly Returns $\%$ Standard Deviation of Monthly Returns $\%$

Initial portfolio $0\mathrm{.}752\mathrm{.}62$

Government bond $0\mathrm{.}42$

Calculate the standard deviation of the new portfolio of the new portfolio $($which includes the government bond$).$