The other day I heard the business reporter on the radio say "Advancing stocks led declining stocks by 7 to 5." That is, 7/12 of all stocks went up for the day, and 5/12 went down.
Now, there are thousands of stocks in the market, so 7/12 is most likely just an approximation to the actual number. My question is, how good an approximation is it? You have enough information to answer the question if you make one reasonable assumption.