1.2007×20082008—2008×20072007
=2007×2008×10001-2008×1007×10001
=0
2.4.2÷0.25÷4
=4.2÷(0.25×4)
=4.2÷1
=4.2
3.2+4+6+8+、、、+96+98+100
=(2+100)×50÷2
=2550
4.1/4×3÷1/4×3
=1/4÷1/4×3×3
=9
5.1/1×3+1/3×5+1/5×7+、、、+1/19×21
=(1/2)×(1-1/3+1/3-1/5+1/5-1/7+.+1/19-1/21)
=1/2×(1-1/21)
=10/21
6.9999×7＋1111×37
=1111×9×7+1111×37
=1111×(63+37)
=1111×100
=111100