Hi All,
We're told that the cost of delivery for an order of desk chairs was $10.00 for the first chaircand $1.00 for each additional chair in the order. We're asked if an office manager placed an order for N desk chairs, is N > 24. This is a YES/NO question. This DS question is a nice example of what's called "a question BEHIND the question."; this idea of finding another way to view the question usually occurs a few times on Test Day and makes those particular questions easier to answer.
Since we know what 24 chairs would cost ($10 for the 1st, $1 for each additional = $10 + $23 = $33), the question BEHIND the question asks "Did the office manager spend more than $33?"
1) The delivery cost for the order totalled more than $30.00.
If it's $31, then the answer to the question is NO
If it's $35, then the answer to the question is YES
Fact 1 is INSUFFICIENT.
2) The average delivery cost of the N chairs was $1.36.
This information is fantastic because we don't actually have to calculate anything. There's only one value of N that will equal $1.36 exactly. If you change the N, then the average changes. Fact 2 would be enough to tell us exactly what N is, so we'd be able to answer the question (and there would be JUST ONE answer).
Fact 2 is SUFFICIENT.
Final answer:
GMAT assassins aren't born, they're made,
Rich
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