When you multiply 2^1990 by 5^1991 you get a product with 1991 digits. What is the sum of all of these digits?
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Anonymous2005-12-07 20:30 (sage)
1990 pairs of twos and fives make 1990 tens, multiplied together.
multiplied by five, something that already had 1991 digits continues to have 1991 digits. It is 5(10^1990), and the sum of the digits is five.