BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Prime number question

Expert replies
Source: — Problem Solving |

by Brent@GMATPrepNow » Mon Apr 01, 2013 3:43 pm
sanaa.rizwan wrote:If n=4p where p is a prime number greater than 2, how many different positive even divisors does n have including n

A.2
B.3
C.4
D.6
E.8
Just pick a possible value for n.
To do so, let p=3 (a prime greater than 2), which means n = 4(3) = 12
The even divisors of 12 are 2, 4, 6 and 12
So, there are 4 even divisors.
Answer = C

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Join the discussion

by hemant_rajput » Tue Apr 02, 2013 10:00 am
sanaa.rizwan wrote:If n=4p where p is a prime number greater than 2, how many different positive even divisors does n have including n

A.2
B.3
C.4
D.6
E.8
general approach here is

for any no. N = 2^x * 3^y * 5^z ...so on, where x, y and z are their power.
then total no. of factors of N will be (x + 1) * ( y + 1) * (z + 1) ... A
then total no. of odd factors will be ( y + 1) * (z + 1) ... B
then total no. of even factors will be A - B
for example

n = 6 = 2 * 3
total no. of factors = (1 + 1) * (1 + 1) = 4
total no. of odd factors = 2
total no. of even factors = 4-2 = 2

This approach is good when you need to find the even or odd factor of larger no.
I'm no expert, just trying to work on my skills. If I've made any mistakes please bear with me.
Join the discussion