①5分之4X2分之1÷3分之1
=2/5÷1/3
=6/5
=1.2
②16分之15÷2分之3-4分之1
=5/8-1/4
=3/8
③2.5X（5分之2-3分之1）+2.1
=2.5×1/15+2.1
=1/6+2.1
=2又4/15
④15分之2÷（1.1-4分之3）+5分之1X5分之3
=2/15÷0.35+3/25
=8/21+3/25
=263/525