factor problem

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 141
Joined: Wed Mar 28, 2007 9:24 pm
Thanked: 2 times
Followed by:1 members

factor problem

by jamesk486 » Wed Apr 11, 2007 1:16 am
X is a prime and y is a positive integer, How many different factors of (2^3)*(x^y) are there?
(1) x=5
(2) y=3

I got stuck in the middle, after figuring out that the number of factors would be (3+1)(y+1)...but someone told me that x could not be 2 or something like that..anyways i'm pretty lost!

User avatar
Legendary Member
Posts: 1275
Joined: Thu Sep 21, 2006 11:13 pm
Location: Arabian Sea
Thanked: 125 times
Followed by:2 members

Re: factor problem

by ajith » Thu Apr 12, 2007 1:51 am
jamesk486 wrote:X is a prime and y is a positive integer, How many different factors of (2^3)*(x^y) are there?
(1) x=5
(2) y=3

I got stuck in the middle, after figuring out that the number of factors would be (3+1)(y+1)...but someone told me that x could not be 2 or something like that..anyways i'm pretty lost!
If 2 is a factor of x the number of factors of (2^3)*(x^y) would not be (3+1)(y+1)

So we need to know x as well as y to determine the number of factors.

:)
Always borrow money from a pessimist, he doesn't expect to be paid back.

Master | Next Rank: 500 Posts
Posts: 141
Joined: Wed Mar 28, 2007 9:24 pm
Thanked: 2 times
Followed by:1 members

by jamesk486 » Thu Apr 12, 2007 6:45 am
I'm still confused...because I thought the answer would be B but its C...

Senior | Next Rank: 100 Posts
Posts: 70
Joined: Sun Mar 18, 2007 9:35 am
Location: mumbai
Followed by:1 members

by RAGS » Thu Apr 12, 2007 7:12 am
Well here as u know the no of factors can be found out by getting the no of prime factors as u said (1+3)(y+1)

statement 1 gives x=5 whickh is not sufficient since u need to know Y

statement 2 gives y=3
here consider the case where x=2 then we have no of factors will be
for 2exp(6) will be (6+1) ie 7
but for x as any prime other than 2 the ans would be (3+1)(3+1) ie 16

but both together solves the problem by giving a value to X
So C

Legendary Member
Posts: 559
Joined: Tue Mar 27, 2007 1:29 am
Thanked: 5 times
Followed by:2 members

by Cybermusings » Thu Apr 12, 2007 7:25 am
Thanks RAGS...your explanation has lifted the cloud