If there are 664,579 prime numbers among the first million positive integers, apporximately what percent of the first 10 million positive integers are prime numbers.

(A) 0.0066%

(B) 0.066%

(C) 0.66%

(D) 6.6%

(E) 66%

解释:

The ration of 664,579 to 10 million is approximately 660,000 to 10,000,000 or 66/1,000=0.066=6.6%

My question is how can I know there are not enough prime numbers between 1,000,000 to 10,000,000 to change the percent to a higher number?