SAT Practice Math Questions: Percentage
The SAT loves percentages, perhaps because math teachers who are sick of the question “Am I ever going to use this stuff in real life?” actually write the math portion of the exam.
With percentages, the answer is yes if you’re taking out a loan (interest rates) or investing the earnings from your part-time job in mutual funds (still interest, but this time it’s a good thing) or buying something on sale (15 percent off the regular price). Percents represent how much of each hundred you’re talking about.
Taking a percentage of a number is a simple task if you’re using a calculator with a “%” button. Just hit the “%” and “´” buttons. For example, to find 60 percent of 35, multiply 60% by 35. The answer is 21. If you’re not blessed with such a calculator, you can turn a percent into a decimal by moving the decimal point two spaces to the left, as in 60% = 0.60. (Other examples of percents include 12.5% = 0.125, 0.4% = 0.004, and so on.) Or turn the percent into a fraction. The “cent” in percent means hundred, (as in a century is 100 years,) so 60 percent literally means, “60 per 100,” or 60/100.
For more complicated problems, fall back on the formula you mastered in grade school:
Now try some examples.
- The value of your investment in the winning team of the National Softball League increased from $1,500 to $1,800 over several years. What was the percentage increase of the investment?
- A. 300
- B. 120
- C. 50
- D. 20
- At one point in the season, the New York Yankees had won 60 percent of their games. The Yanks had lost 30 times and never tied. (As you know, there are no ties in the world’s noblest sport, baseball.) How many games had the team played?
- A. 12
- B. 18
- C. 50
- D. 75
Answers and explanations
- D. The key here is that the number 1,800 shouldn’t be used in your formula. Before you can find the percent of increase, you need to find the amount of increase, which is 1,800 – 1,500 = 300. To find the percentage of increase, set up the following equation. Cross-multiply to get 1,500x = 30,000. Dividing tells you that x = 20 percent.
- D. Did you find the catch? The winning percentage was 60 percent, but the question specified the number of losses. What to do? Well, because ties don’t exist, the wins and losses must have represented all the games played, or 100 percent. Thus the percentage of losses must be 100% – 60%, which is 40%. Putting the formula to work:
As always, cross-multiply: 40x = 3,000, and x = 75.