Non-integer calculations in bash

Shell Programming and Scripting
1

I'm new at scripting but I thought I was getting pretty good at it. I've hit a snag. I try to use expr to compute a fraction say: expr 3 / 4, and I'm getting zero. I guess it's just truncating to the integer, in this case 0, but I need the decimal 0.75. What can I do to compute this value in order to assign it to a variable?

2 
echo 'scale=2; 3/4' | bc
3

Thanks a lot!