If you're using bash, you'd better use an here string instead of a pipe as in:

bc <<< "scale=2;$var1/$var2"

This will save you a subshell.

Then, to store the output of a command, use a command substitution:

answer=$(bc <<< "scale=2;$var1/$var2")

Edit.

If you want something even cooler than bc, here's dc (reverse polish calculator):

answer=$(dc <<< "2k $var1 $var2/p")

As is the case with most programming, solving the problem was extremely hard. I had to study a bunch about Bash variables, and how to use export and source (or the POSIX dot operator, .), and how bash loads, and what interactive -i bash mode was, etc etc.

I found man bash and man test to also be useful. Here's how to do what I want to do, which is:

1. Write a script to open 3 tabs.
2. cd into a different folder in each tab (ie: run a unique command).
3. get each tab to have a unique title by modifying its local PS1 variable
4. Ensure each tab stays open after the script is run

1st, add this to the bottom of your ~/.bashrc file:

# Function to allow a user to arbitrarily set the terminal title to anything
# Example: `set-title this is title 1`
set-title() {
    # Set the PS1 title escape sequence; see "Customizing the terminal window title" here: 
    # https://wiki.archlinux.org/index.php/Bash/Prompt_customization#Customizing_the_terminal_window_title
    TITLE="\[\e]2;$@\a\]" 
    PS1=${PS1_BAK}${TITLE}
}

# Back up original PS1 Prompt 1 string when ~/.bashrc is first sourced upon bash opening
if [[ -z "$PS1_BAK" ]]; then # If length of this str is zero (see `man test`)
    PS1_BAK=$PS1 
fi

# Set the title to a user-specified value if and only if TITLE_DEFAULT has been previously set and
# exported by the user. This can be accomplished as follows:
#   export TITLE_DEFAULT="my title"
#   . ~/.bashrc
# Note that sourcing the ~/.bashrc file is done automatically by bash each time you open a new bash 
# terminal, so long as it is an interactive (use `bash -i` if calling bash directly) type terminal
if [[ -n "$TITLE_DEFAULT" ]]; then # If length of this is NONzero (see `man test`)
    set-title "$TITLE_DEFAULT"
fi

2nd, create this script to open 3 unique tabs with 3 unique cd commands and 3 unique titles:

open_tabs.sh:

gnome-terminal --tab -- bash -ic "export TITLE_DEFAULT='title 1'; cd ..; exec bash;"
gnome-terminal --tab -- bash -ic "export TITLE_DEFAULT='title 2'; cd ../..; exec bash;"
gnome-terminal --tab -- bash -ic "export TITLE_DEFAULT='title 3'; cd ../../..; exec bash;"

Now open up a terminal and run the open_tabs.sh script:

./open_tabs.sh

Voila! It's magical! These 3 new tabs are now shown at the top of my terminal, and each has done the proper cd command I set, and each has the proper title I set!

This will all be placed into my dotfiles project: https://github.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles.

Full and final solution: see here: Open Terminal with multiple tabs and execute application