This is a GMATprep question, I believe.
So you're trying to find out if rst = 1.
1. tells you that rs = 1. Obviously, since you don't know anything about t, you can't say if rst = 1. For all you know, t = 1 or t = 1000.
2. again, you don't know anything about r, so this is not sufficient either.
Put both together to get that r*(s^2)*t = 1. This means that rst = 1/s. Now, 1/s = 1 only when s = 1. If s is not 1, then the whole thing falls apart. Take a simple example to prove that.
Say r = t = 4 and s = 4. This means indeed that r(s^2)t = 1, but rst = 4*1/4*4 = 4, which is different from 1.
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Source: Beat The GMAT — Data Sufficiency |
