Now that you’ve gotten a little more confident, we’re going to give you the opportunity to practice "without the training wheels

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问题 Now that you’ve gotten a little more confident, we’re going to give you the opportunity to practice "without the training wheels." When you want to check your work, you can turn to the solutions at the end. If you aren’t familiar with some of the mathematical concepts, make a note to pay particular attention to that chapter in this book; this practice set covers a wide range of topics tested on the GMAT.
   On all data sufficiency problems, the answer choices are the same (as you’ve learned). We’ve put them here for your reference.
   A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
   B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
   C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
   D. EACH statement ALONE is sufficient.
   E. Statements (1) and (2) TOGETHER are NOT sufficient.
If the square root of t is a real number, is the square root of t positive?
   (1) t>0
   (2) t2>0

选项

答案E

解析 This question is looking for a definite yes or no answer. Statement (1) is not sufficient since all it tells us is that t is a positive number. Unless the radical sign () is used, a positive number has two square roots, a positive root and a negative root. For example, if t is 4, then it has two square roots, 2 and -2. So we can eliminate A and D.
   With statement (2) alone, we don’t get much more information; all it really tells us is that t is a positive number (it cannot be negative, since the square root of a negative number is a complex number, not a real number). So again, t could be 4, and its root could be either positive or negative. So we can eliminate B. Putting them both together doesn’t tell us whether the square root of t is positive either, so our answer has to be E.
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