解:(1)99×101,
=99×(100+1),
=99×100+99,
=9900+99,
=9999;
(2)335+270+130+265,
=(335+265)+(270+130),
=600+400,
=1000;
(3)625-180-225,
=(625-225)-180,
=400-180,
=220;
(4)35×99+35,
=35×(99+1),
=35×100,
=3500;
(5)175×55+25×55,
=(175+25)×55,
=200×55,
=200×(50+5),
=1000+100,
=1100;
(6)50×25×20×40,
=(50×20)×(25×40),
=1000×1000,
=1000000.
分析:(1)把101看做100+1,运用乘法分配律简算;
(2)(3)运用加法交换律与结合律简算;
(4)(5)运用乘法分配律简算;
(6)运用乘法交换律与结合律简算.
点评:完成本题要注意分析式中数据,运用合适的简便方法计算.