GMAT Data Sufficiency (DS) | Re: If p + q = 400 and p < q, is p + q < r + s?

A.
We're trying to see if 400<r+s

1. p+r+s=600
p=600-r-s
substitite P into p+q=400
600-r-s+q=400
200+q=r+s
From here we get is p+q<200+q or is p<200? We know from what is given that p<q and therefore less than 200 so suff
2. q+r>400
r>400-q
We can substitute q for 400-p from the equation given and get
r>400-(400-p) and then get r>p. We know nothing about S

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