1989×1999-1988×2000.

问题描述:

1989×1999-1988×2000.

1989×1999-1988×2000
=1989×(2000-1)-1988×2000,
=1989×2000-1989×1-1988×2000,
=(1989-1988)×2000-1989,
=1×2000-1989,
=2000-1989,
=11.