原式=15/3x1/5+1/5x2-1/5=1+2/5-1/5=1+1/5=1又1/5又=1.2
=5×1/5+1/5×2-1/5=(5+2-1)×1/5=6×1/5=1.2
15/3×1/5+1/5×2-1/5=1/5×(5+2-1)=6/5=1.2