what is 10000x100000?

The answer is 1 billion, or 1 followed by 9 zeroes, read as 1,000,000,000.

The general rule for multiplying 10s is to count the zeroes... In this case, there are a total of 9 zeroes between the two numbers, which means the answer will be 1 (1x1 is 1) followed by nine zeroes.

A scientist would give you one of these answers...

http://www.wolframalpha.com/input/?i=10000X100000

Depends whether you are British or American!
In Britain it would be one thousand million. A British Billion is, correctly, 1 followed by 12 zeroes although these days we appear to have accepted the American Billion as a standard.

No base is stated for the way in which these numbers are written. They might be any base.
If they are binary as looks quite feasible, this would be equivalent to the decimal 16 times 32, or 512. In binary the answer looks the same, 1000000000, but there is no name for this number. The trick of adding the zeros is the same in any base.
http://www.binarymath.info/multiplication-division.php

the answer is 1 billion.....1,000,000,000