Those expressions are evaluated to a number.
Integer
shell$(( 5+2 ))
$(( 5-2 ))
$(( 5*2 ))
$(( 5/2 ))
$(( 5%2 ))
$(( 5**2 ))
(( count+=1 ))
Decimal
Package bc is required.
shell'10.5+2.5' | bc -l
'10.5-2.5' | bc -l
'10.5*2.5' | bc -l
'10.5/2.5' | bc -l
'10.5^2.5' | bc -l
'sqrt(10.5)' | bc -l