=9999x(10000-1)
=9999x10000-9999x1
=99990000-9999
=9980001
[2]777777x99999÷111111÷11111
=(777777÷111111)x(99999÷11111)
=7x9
=63
[3](25+25x99)x16
=(1+99)x25x4x4
=100x100x4
=40000
[4]6230-1-2-3-4-…-99-100
=6230-(1+2+3+4+……+99+100)
=6230- 5050
=1180
[5]100+99-98-97+96+95-94-93+…+4+3-2-1
=（100+99-98-97）+（96+95-94-93）+…+（4+3-2-1） (每4個連續的分成壹組,得數是4,壹***25組）
=4×25
=100