1、3-1/3-1/3÷3
=3-1/3-1/9
=3-(3/9+1/9)
=23/9
2、15/16+(7/16-1/4)÷1/2
=15/16+3/16÷1/2
=15/16+6/16
=21/16
3、1/5÷[(2/3+1/5)*1/13]
=1/5÷[13/15*1/13]
=1/5÷1/15
=3