(12.5 +2.5)×0.8×0.4=15×0.8×0.4=15×0.4×0.8=6×0.8=4.8
原式=15x4/5x2/5=24/5
(12.5+2.5)×0.8×0.4=12.5×0.8×0.4+2.5×0.4×0.8=10×0.4+1×0.8=4.8