数学 面粉5公斤,做饼用去10分之1,做蛋糕用去5分之2,共用去面粉多少公斤?

共用去面粉:
5*1/10+5*2/5
=5/10+2
=2又5/10
=2又1/2
=2.5(kg)

面粉5公斤,做饼用去10分之1
= 5 x 1/10
= 0.5 Kg

做蛋糕用去5分之2
=5 x 2/5
= 2 Kg

共用去面粉多少公斤?
= 2 + 0.5 Kg
=2.5 Kg

总共用去

5X1/10+5X2/5
=1/2+2
=2.5KG

QED