0.25×13.7×0.4=0.25×0.4×13.7=1×13.7=13.7
先算0.25乘0.4等于0.1，再乘13.7等于1.37
=0.25*0.4*13.7=1.37
（0.25x0.4）x13.7=0.1x13.7=1.37
