Unclear numbers crunching


From the quote below,
How did you get to 15%?
How did you then get to “~500 Million new queries”?

" A: Lets first look at the amount of new data we generate every day. 15% of the search queries are new for Google ( ~500 Million new queries ). Assuming 25 letters on average per query, we will 12.5G new data per day.
Assuming, we have accumulated queries over the last 10 years, the size would be 12.5 * 365 * 10 G which is approximately 50TB."