0.02+0+04+0+06+…+19.96+19.98 简便计算错了，是0.02+0.04+0.06+…+19.96+19.98

0.02+0+04+0+06+…+19.96+19.98 简便计算错了，是0.02+0.04+0.06+…+19.96+19.98
0.02+0+04+0+06+…+19.96+19.98 简便计算
错了，是0.02+0.04+0.06+…+19.96+19.98

0.02+0+04+0+06+…+19.96+19.98 简便计算错了，是0.02+0.04+0.06+…+19.96+19.98
0.02+0.04+0.06+…+19.96+19.98
=(0.02+19.98)×999/2
=20×999/2
=10×999
=9990

19.98/0.02=999
即求首项为0.02，公差为0.02，项数为999项的等差数列之和
0.02+0.04+0.06+…+19.96+19.98
=（0.02+19.98）*999/2
=9990