We have measured the branching fractions for $B\to \overline{D}X$, $B\to \mathrm{DX}$, and $B\to \overline{D}X{\ell }^{+}\nu$. From these results and some previously measured branching fractions, we obtain $B(b\to c\overline{c}s)=(21.9\pm 3.7)\%$, $B(b\to \mathrm{sg})<6.8\mathrm{}\%$ at 90% C.L., and $B(D^0\to K^{-}{\pi }^{+})=(3.69\pm 0.20)\%$. Implications for the “ $B$ semileptonic decay problem” (measured branching fraction being below theoretical expectations) are discussed. With the increase in the value of $B(b\to c\overline{c}s)$ due to $B\to \mathrm{DX}$, the discrepancy is no longer statistically compelling.

• Received 23 October 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.1150