GMATPREP question, should be studied

[tanviet]

n is an integer, r is redundant when (n-1)(n+1) is divided by 24. what is value of re

1,n is not divided by 2

2,n is not divided by 3

[papgust]

Please recheck your question and post it clearly

[neoreaves]

n is an integer, r is redundant when (n-1)(n+1) is divided by 24. what is value of re

1,n is not divided by 2

2,n is not divided by 3

Ok so assuming redundant was meant to be remainder and value of r is asked instead of re

24 = 3x8 so lets keep that in mind

1) n is not divisible by 2

That means (n-1) and (n+1) are both divisible by 2. Infact one of them would be divisible by 4. Thus (n-1)(n+1) will be divisible by 8. But we dont know if n will be divisible by 3 or not. If it is then r = 0 otherwise r is not equal to 0.

2) Similarly (n-1) or (n+2) is divisible by 3. However, we dont know if n is a prime number or an even number. To divide (n-1)(n+1) completely we need a 3 and an 8. This statement doesnt give us enough information

c) From 1) and 2) (n-1)(n+1) is divisible by 8 and 3. So r =0.


Answer should be C

[tanviet]

---2) Similarly (n-1) or (n+2) is divisible by 3. However, we dont know if n is a prime number or an even number. To divide (n-1)(n+1) completely we need a 3 and an 8. This statement doesnt give us enough information ----


nevevares

pls, explain above thing.

[tanviet]

I think we should explain 2) as following

n is not divided by 3

so

n-1, or n+2 or n-2 or n+1 is divided by 3

that mean (n-1)(n+1) is divided by 3

from 1) we have (n-1)(n+1) is divided by 8

from 2), we have (n-1)(n+1) is divided by 3.

so both make it divided by 24, r=0

C is correct