Question

1.9➕1.99➕1.999➕1.9999➕......➕1.9999999999等于多少？

Answer 1

1.9➕1.99➕1.999➕1.9999➕......➕1.9999999999
=（2-0.1）+（2-0.01）+。。。+（2-0.0000000001）
20-0.1111111111
=19.8888888889

Answer 2

原式=(2-0.1)+(2-0.01)+(2-0.001)+(2-0.0001)+……+(2-0.0000000001)
=2×10-(0.1+0.01+0.001+……+0.0000000001)
=20-0.1111111111
=19.8888888889