Number properties question- MGMAT Guide

I didnt get what confuses u

t = s - 3 => t+s=3 3 is odd

LalaB wrote:I didnt get what confuses u

t = s - 3 => t+s=3 3 is odd

This step is wrong;

put any s and t you will odd for all combination.
Hence ODD

killer1387 wrote:

LalaB wrote:I didnt get what confuses u

t = s - 3 => t+s=3 3 is odd

This step is wrong;

put any s and t you will odd for all combination.
Hence ODD

ehm, actually it is 3= s-t (my fault)

3(odd)=even-odd or odd=odd-even

then
even+odd=odd

HG10 wrote:If t = s - 3, what is s + t?

Answer the question as ODD, EVEN or CANNOT BE DETERMINED

Source: Manhattan GMAT Number Properties Strategy Guide, q. 12, pg. 33

OA: ODD

First off, I'm assuming that the question states that s and t are integers?

With that assumption in mind, his question is testing your knowledge of odds and evens. Specifically -- in this case -- they are testing your knowledge of the additive qualities of odds and evens.

t = s - 3

Or...

s = t + 3

Whenever you add an odd number (3) to another integer, the result will always have the opposite parity (aka odd to even or even to odd). This means that s will always be the opposite of t.

So, when you add together s and t, you are always adding an even and an odd, which will always be ODD.

If t = s - 3

therefore,
s+t=2s -3 ...... adding s both sides.
now 2s is always even and if you subtract an odd number from even you always get an odd.

Hence, answer is ODD.

Guys, thank you all for the solutions!

HG10

please type the question properly, as first of all we are supposed to assume that both s and t are positive integers. Only then they can be odd...

If even one is fraction then it can lead to cannot be determined.

Kindly post the question properly as you do it in the real test...

People are studying here, with the timer on...