GMAT Question Bank Problem

[bhumit920]

I really can't crack this one; any help would be really appreciated.
If q, r, and s are consecutive even integers and q < r < s, which of the following CANNOT be the value of s2 - r2 - q2?


A. -20
B. 0
C. 8
D. 12
E. 16

[gagandeepm]

Assume the even numbers to be 2n+4(s), 2n+2(r), 2n(q).
solving for s2-q2-r2 = 12 - 4n(n-2)

Now check for the choice a to e which will not yield a integer value for n.

Except C all other yield a integer value of n.
So the right answer is C

[tim]

thanks; this is a great explanation. however, bhumit, this is very close to the answer given in our materials, so can you let us know whether this was an adequate explanation?

[dibrushi]

Hi! What about n=0??We can not have n zero, can't we??so shouldn't it be 12?

[tim]

why is n not supposed to be 0?

[mmsmoney]

The ans is A

Substitute the foll examples for the three integers

2 4 6 - will give 0

-2 -4 -6 - will give 16

2 0 -2 - will give 8

0 -2 -4 - will give 12

you cant get a negative value at all thats the trick

[tim]

You’re not substituting correctly. Try again..

[mmsmoney]

oh am sorry Mr Tim i thought it was 2 multiplied by s...

didn't notice it as a "square"...

anyway am wrong, if it was multiplied by 2 all options are possible..

its better if u remove that post so others wont be confused...

[jnelson0612]

oh am sorry Mr Tim i thought it was 2 multiplied by s...

didn't notice it as a "square"...

anyway am wrong, if it was multiplied by 2 all options are possible..

its better if u remove that post so others wont be confused...

No worries! Other students will learn from your error. Glad you caught it!