5.4x19.9x0.54
=5.4x19.9x5.4×0.1
=5.4×（19.9+0.1）
=5.4×20
=108不对5.4x19.9x0.54=58.0284你的题出错了，要不然无法简便运算5.4x19.9+0.54=5.4x19.9+5.4×0.1=5.4×（19.9+0.1）=5.4×20=108