How do you derive a decimal from a math operation involving a variable?

I'm trying to find derive SCALEFACTOR which is basically 10000/(sum of 4th column in a file). How do I get a decimal from the output? Appreciate any help in advance.

#!/bin/bash

FILES=/path/to/files/*;
for f in ${FILES}
do
    echo $f
    COLTOTAL="$(awk '{sum += $4} END {print sum}' $f)"
    echo "total: ${COLTOTAL}"
#    SCALEFACTOR=`expr 10^5 / $COLTOTAL`
    B=10000
    SCALEFACTOR=$((B / ${COLTOTAL}))
#    echo "scale=5; ${SCALEFACTOR}" | bc
    echo ${SCALEFACTOR} | bc -l
done