0.25*28=（0.25*4）*7=1*7=7
0.25×28=0.25×(4×7)=(0.25×4)×7=7
0.25×28=0.25×(4×7)=(0.25×4)×7=1×7=7
0.25=1/41/4 *28 =7
0.25x4x7=1x7=7
