  We study the current estimates of $B_c\to B_s \pi$ to extract the
fragmentation fraction $f_c/f_s$ at the LHCb. A rather robust estimate of
$Br(B_c\to B_s \pi)$ based on factorization and lattice results for the form
factor gives $f_c/f_s \sim 0.056$ with a $16\%$ error. We also revisit the
extraction of $f_s/f_d$ using $B\to D\pi$ instead of the theoretical cleaner
but more suppressed channel $B\to DK$. We also find a tension on the
predictions of $Br(B_c\to J/\psi \pi)$ and $Br(B_c\to B_s\pi)$ considering the
measurements of these modes at LHCb, and find that, within a $23\%$
uncertainty, only the lower end of the current prediction range $Br(B_c\to
J/\psi)\sim 0.4\% - 1.7\%$ would be consistent with the LHCb measurements.
