3.9*7.8+39*0.12+3.9
问题描述：
3.9*7.8+39*0.12+3.9
=
=
••••••递等式啊!
答
3.9×7.8+39×0.12+3.9
=3.9×7.8+3.9×1.2+3.9×1
=3.9×(7.8+1.2+1)
=3.9×10
=39