①-91÷13 =-(91/13)=-7
②-56÷（-14）=56/14=4
③16÷（-3）=-16/3
④（-48）÷（-16）=48/16=3
⑤4／5÷（-1）=-4/5
⑥-0.25÷3／8=-1/4*8/3=-2/3