LearnHub

Join LearnHub

Community

GMAT 2009

DS question ( factors ) (Discussion)

rneve said – Sun, 19 Apr 2009 04:09:19 -0000 ( Edit Link )

If n is a positive integer and r is a reminder when (n-1)(n+1) is divided by 24 , what is the value of r ? 1) 2 is not a actor of n 2) 3 is not a actor of n

ANS IS {C}

Anyone wants to explain?

Actions

Respond

Author: rneve; Authority 80

Vote

Current Rating: 0; Rate Up; Rate Down

No Votes

Indicar said – Mon, 20 Apr 2009 10:53:45 -0000 ( Flag Edit Mark / Unmark Best Link )

Hi Raju, Classic example. i can imagine it’s not simple hwile giving exam when U just hv 2 mins for this. Still, a try. My way of solving this. 1. If n is not divisible by 2 then all even no. are out of consideration. So now consider 3 then the value comes out not divisible by 24. But 5, 7, 11 and other multiples come out good for this. But you have to rule out A, D. 2.I looked at second condition and then considered even no.s but then outcome of calculation comes out to be odd no. which cannot be divisible by 24. But again consider 5,7,11 and you get answer. But for now you have to rule out B & D. Now finally consider 5 as n. So n-1=4, n+1=6, multiplying both we get 24 which is divisible by 24, reminder is 0. So n is not divisible by either 2 or 3 which r conditions a & b respectively but on considering both you get answer. SO answer is C.

Others can comment if they have better way to answer this query.

Actions