（6分之1-12分之1）×24-5分之4
=1/6×24-1/12×24-4/5
=4-2-4/5
=2-4/5
=1.2
7.8×2.5+78×0.75
=7.8×2.5+7.8×7.5
=7.8×（2.5+7.5）
=7.8×10
=78