2/5x2/10+9/10x0.4-2除以5x1/10,
问题描述：
2/5x2/10+9/10x0.4-2除以5x1/10,
x:是乘,尽快,我明天要演讲了
答
2/5x2/10+9/10x0.4-2除以5x1/10
=2/5×2/10+9/10×2/5-2/5×1/10
=2/5×1/10*(2+9-1)
=2/5×1/10×10
=2/5