(1)800 ÷
4
5 =1000(本);
答:科技书有1000本.
(2)800×(1+
1
5 ),
=800×
6
5 ,
=960(本);
答:科技书有960本.
(3)(800+80) ÷
11
20 ,
=880÷
11
20 ,
=1600(本);
答:科技书有1600本.
(4)800×
3
4 ÷60%,
=600÷60%,
=1000(本);
答:科技书有1000本.
(5)800÷40%-800,
=2000-800,
=1200(本);
答:科技书有1200本.
故答案为:800 ÷
4
5 ,800×(1+
1
5 ),(800+80) ÷
11
20 ,800×
3
4 ÷60%,800÷40%-800.