Arithmetic Operations in bash

Addition:
$ x=1
$ y=`expr $x + 2`
$ echo $y
3

Subtraction:
$ x=5
$ y=`expr $x - 2`
$ echo $y
3

Multiplication:
$ x=5
$ y=`expr $x \* 2`
$ echo $y
10

Division:
$ x=12
$ y=`expr $x \/ 3`
$ echo $y
4