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.
What is the ratio of 2a to b
(1)
(2) a+b=5
参考答案：A
解析：Statement (1) says that
We are looking for the ratio
. If you substitute 2 for
in that ratio, you get 2 times 2, which equals 4. Statement (1) is sufficient. Cross off B, C, and E. How about statement (2) Remember, you have to forget about the information you got from statement (1). Since there are several values for a and b that would add up to 5, let’s try a couple of variations to see if we always get the same ratio. If a is 3 and b is 2, the ratio of 2a to b would be 6:2 or 3:1. But if we used a=2 and b=3 instead (and nothing tells us that we can’t), the answer to the question stem becomes 4:3. When we can get different answers, we can tell the statement is not sufficient, so we can eliminate D. A is the correct answer.