2.5×【5分之2-3分之2】+3又6分之1
=5/2×【5分之2-3分之2】+3又6分之1
=5/2×2/5-5/2×2/3+3又6分之1
=1-5/3+3又6分之1
=-2/3+3又6分之1
=19/6-4/6
=15/6
=5/2
=2.5