Explanation
We have a combined rate question here. The rates involve
air purified per hour, but we aren't given any quantities or measures of air in
the prompt, just "parts" of the floor, so we cannot calculate a rate for either
machine yet. On to the statements, separately first.
Statement (1) gives us the rate of one of the machines.
But we don't know the rate of the first machine. So we can imagine two cases,
one in which the first machine is much slower than the second, and another in
which the first machine is much faster than the second. In those two cases,
we'll get quite different results for how long it would take the first machine
to do it all alone. So Statement (1) is insufficient.
In the second statement, we get a comparative measure of
the amounts of air these things purified. If
purified x amount of air in 4 hours, then
Statement (2) is telling us that
It also means that the total air on the floor is 2.5x, since the combined efforts of the two
machines covered the whole floor. Working with the rate for
, we have
To double-check that we're right, we can do the same
calculation for
:
It checks out that it would take less time for
--namely,
or
hours--to do the whole floor than
, since
is faster.
Statement (2) is sufficient.
The correct answer is (B).
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