GMAT考试之Kaplan数学策略

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Sharpen Your Math Skills
Whether you're thinking of a career as an accountant or just trying to balance your checkbook, you face math in some way, shape or form every single day.
Not only are strong math skills important to doing well in school, they are also critical to your success in everyday life. You have to pay bills; plan for a financially secure future; pay taxes; and you probably split the cable bill with your roommate.
A Language All Its Own
Think of mathematics as its own language. Just like the language of words, grammar, and punctuation, the language of math is precise. It helps to know as much of the rules, vocabulary, and methods as possible to make informed decisions about problems on a test or in day-to-day life.
So the main lesson here is to look at the big picture. Look at how individual parts of a problem relate to a whole. You'll gain a better understanding of the concepts behind the numbers. And in the process, you'll gain a better understanding of the world around you.
Practice Questions
Try out the practice problems below and see how you do. Each represents some important math concepts that are critical to success at school, on the job, and in life. The answers are below.
1. In May, Gina sold 40 percent more magazine subscriptions than she had in April. In June, she sold 20 percent more subscriptions than she had in May. The number of magazine subscriptions Gina sold was what percent greater in June than in April?
(A) 60
(B) 64
(C) 68
(D) 72
(E) 80
2. Directions: Answer (A) if the quantity in Column A is greater; (B) if the quantity in Column B is greater; (C) if the two quantities are equal, or (D) if the relationship cannot be determined from the information given
Square A has sides of length x and square B has sides of twice this length.
Column A
Area of square A
Column B
Half the area of square B
Answers and Explanations
1. The correct answer is (C). Since we are not given a number for how many subscriptions Gina sold in April, let's pick a number. Let's pick 100. When you have a percent problem and numbers are not provided, you should always pick 100 because it is easy to work with.
In April, let's say Gina sold 100 magazines. We are told that in May she sold 40 percent more magazine subscriptions than she had in April so the number she sold in May is 100 plus 40 percent of 100, or 140. In June, Gina sold 20 percent more subscriptions than she did in May. Well, in May she sold 140 subscriptions and 20 percent of 140 is 20 percent times 140 or 28.
Therefore, in June, Gina sold 140 plus 28 subscriptions, or 168 subscriptions. The percent that the number of magazine subscriptions sold in June, 168, is greater than the number sold in April, 100, is 68 percent, answer choice (C).
2. The correct answer is (B). In this question, we are given that one square, A, has sides of length x and a second square, B, has sides of twice this length (or 2x), and we are asked to compare the area of A to one half the area of B. The first thing you should do is draw a diagram. (You should draw a diagram when you are not provided with one or when you are given one that is not drawn to scale.) If you draw the squares somewhat carefully, the answer becomes obvious.
Figured out mathematically, the area of a square is the side squared. Column A will, then, yield a square with area x2. Column B will yield a square with area 4x2. x2 compared to 2x2 gives us an answer choice of (B) because 2x2 is greater. You could have picked numbers for the sides of the squares and would have still come out with Column B being greater.