GMAT Data Sufficiency (DS) | Re: Is wp+st>0?

(1) ws + pt > 0
we have no info about signs of all 4 variables..
Consider w=p=1 & s=3,t=2
then we have ws + pt > 0 also we have a YES to our ans.

But
w=-1,s=-2 , p=1 , t=3
then we have ws + pt > 0 but we have a NO to our ans.
Insuff....

similarly statement (2) is insuff..

Combining we get
adding both ws+wt+pt+ps>0
w(s+t)>p(s+t)
(w+p)(s+t)>0
consider w=p=s=t=-1 for Yes
w=2
...

---