24乘五分之二加75除以2.5加0.4
=24乘五分之二加75×0.4加0.4
=（24+75+1）×0.4
=100×0.4
=40我的2.5呢，谁吃了？0.4乘0.4=0.16呀75÷2.5=75×0.4