-72*(1/4-5/9+7/12)/(-2)

问题描述:

-72*(1/4-5/9+7/12)/(-2)

=-72X(9/36-20/36+21/36)/(-2)
=-72X(-11/36+21/36)/(-2)
=-72X(10/36)/(-2)
=-72X(-5/9)
=40