1234567898765432123456789876543212345678987654321x999=?

1234567898765432123456789876543212345678987654321x999
=1234567898765432123456789876543212345678987654321x(1000-1)
=1234567898765432123456789876543212345678987654321x1000+1234567898765432123456789876543212345678987654321
=1234567898765432123456789876543212345678987654321000+1234567898765432123456789876543212345678987654321

1234567898765432123456789876543212345678987654321x999=1.23333333*10^51

要解這問題，最好是考慮一些會重覆的部分，可參考下面的做法：

1234567898765432123456789876543212345678987654321x999
= 1234567898765432123456789876543212345678987654321000
- 1234567898765432123456789876543212345678987654321
= 1234567898765432123456789876543212345678987654321234
- 1234567898765432123456789876543212345678987654321
- 234

...........repeating group
........./-----------------------\/------------------------\/-----------------------\
1234567898765432123456789876543212345678987654321234
-.....1234567898765432123456789876543212345678987654321
--------------------------------------------------------------------------------------------
1233333330866666691333333086666669133333308666666913
-.................................................................................................234
--------------------------------------------------------------------------------------------
1233333330866666691333333086666669133333308666666679
==============================================
So we need to calculate 5678987654321234 - 2345678987654321
= 3333308666666913. Then fill it in each repeating group. After that
we append it with the result 1234 - 1 = 1233 in the first four digit.
Then we minus 234 and we get the result.

所以答案是 1233333330866666691333333086666669133333308666666679.

利用這做法可以計算其他類似的算式，例如：
1234567898765432123456789876543212345678987654321x99999=? 式者
12345678987654321234567898765432123456789876543212345678987654321x999=? 等等

2007-12-20 21:24:28 補充：
我認為這個並非一個最佳的回答，因為它根本還沒有找出答案，既然要成為一種新知識，最起碼都要能夠有一個正確且確定的答案吧。請發問者自選答案前，應仔細考量一下所選擇的最佳答案是否合適。

12345678987654321234 56789876543212345678 987654321000
- 12345678987654321234 56789876543212345678 987654321
=12333333308666666913333330875555580244444197555555679

1.23333333E+51

1234567898765432123456789876543212345678987654321x999=1234567898765432123456789876543212345678987654321x999