How many odd, positive divisors does 640 have? Choose the correct option.
A) 6	B) 8	C) 12	D) 15	E) 24
Make a prime factorization of a number: 540=2^2*3^3*5 --&gt; get rid of powers of 2 as they give even factors --&gt; you'll have 3^3*5 which has (3+1)(1+1)=12 factors.   Another example: 60=2^2*3*5 it has (2+1)(1+1)(1+1)=12 factors out of which (1+1)(1+1)=4 are odd: 1, 3, 5 and 15 the same # of odd factors as 60/2^2=15 has.   Answer: 12.
<result>C</result>
How many odd, positive divisors does 640 have?