=（1/24-3/8）*24
=1/24*24-3/8*24
=1-9
=-8
简便计算（1/4+1/6-3/8）×24=1/4x24+1/6x24-3/8x24=6+4-9=1
（1/4×1/6-3/8）×24=(1/24-9/24)×24=1-9=-8
