原式=3/8x33+66x37.5%+0.375=0.375x33+66x0.375+0.375x1=0.375x(33+66+1)=0.375x100=37.5
3/8×33+66×37.5%+0.375=3/8×（33+66+1）=3/8×100=37.5
