5237+3997
=5237+4000-3
=9237-3
=9234
6453--1998
=6453-2000+2
=8453+2
=8455
17.42--5.87+2.58--4.13
=（17.42+2.58）-（5.87+4.13）
=20-10
=10
9.728/3.2/5
=9.72÷（3.2×5）
=9.72÷16
=0.6075