Explanation
We go ahead and sling an equation onto our note board when
we read the question:
. We need to find S. We might do it by getting two more independent equations
involving these variables, to satisfy the n
variables, n equations. Or, we
could find S by learning the value of
. Let's turn to the statements, separately first.
Statement (1) tells us that
. We have only two equations, so by the rule we
don't have enough to solve exhaustively. We will check for fortuitous algebra.
That would involve finding
. However, in an attempt to isolate
on one side
of this statement we end up with
. Substituting that yields nothing helpful.
Therefore, Statement (1) is insufficient.
Statement (2) says that
. Again, we have only two equations for three variables. But fortuitous algebra is afoot. We can
rewrite this statement as
and
substitute in the order equation to obtain
from
which we can solve for S. We can
answer the question definitively, so Statement (2) is sufficient.
The correct answer is (B).
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