How to eliminate obviously wrong answer choices
If a choice is so outrageous that it couldn’t possibly be the correct answer, you should eliminate it from consideration. For example, the length of a rectangle can never be greater than the rectangle’s perimeter. A person’s age years ago can’t be greater than his or her current age. The mean of a set of data can never be greater than the highest number. These are just some examples of impossibilities you can readily notice.If 3j = 90, what is the value of j?The correct answer is Choice (B). You can find the answer by solving the equation.A. 270
B. 30
C. 60
D. 120
E. 3
To help ensure you get the correct answer, you can eliminate Choices (A) and (D) because both of those choices are greater than 90. You have to multiply 3 by a positive number to get 90, and no positive number is greater than 3 times itself. Eliminating those choices leaves you with three choices to consider instead of five. Choices (C) and (E) are randomly incorrect.
The radius of the preceding circle is 12 meters. What is the circumference of the circle?The correct answer is Choice (A). The formula for the circumference of a circle is C = 2πr. Substituting 12 m for r, you get 2π(12 m) = 24π m. You can eliminate Choice (C) right away because neither π nor a decimal number, which would result from multiplying 12 by a decimal approximation of π, is in the answer. Another reason Choice (C) can be eliminated is because the radius of a circle can’t possibly equal the circle’s circumference. Multiplying by 2π can never be the same as multiplying by 1; 2π is not equal to 1, and it never will be, as far as we know. Choice (B) can be eliminated because multiplying by π is not the same as multiplying by 2π. You can also eliminate Choice (E) because the number that precedes π in a representation of a circumference can’t be less than its radius unless different units are used. Multiplying a positive number by 2π has to result in an increase. The three eliminations leave you with Choices (A) and (D), and that puts you closer to the right answer. Choice (D) is incorrect because it is the area of the circle, not the circumference, except with m instead of m2. If the unit were m2, you could eliminate it right away because circumference is not properly expressed in square units.A. 24π meters
B. 12π meters
C. 12 meters
D. 144π meters
E. 6π meters
Avoid the most common wrong answers
Other choices to watch out for and be ready to eliminate are the ones that result from the most common calculation mistakes. Memorizing the rules for all the math topics you’ll face on the Praxis is important for avoiding these common mistakes.For geometry questions, some of the most common mistakes involve getting formulas confused, such as area and circumference. If you have a question about the area or circumference of a circle, you may have an answer choice that gives you the number involved in a measure about which you’re not being asked. Be ready to avoid such answers.
Also remember the difference between the interior angle sums of triangles and quadrilaterals. Choices may be the result of using the wrong number. Confusion between supplementary and complementary angles is common, and so is confusion between formulas for surface area and volume. Forgetting the formulas for the volume of pyramids and cones also happens often.
As for algebra and number and quantity questions, losing track of the fact that a number is negative is one of the most common mistakes. The distributive property is very frequently used improperly. Remember that the term right before the parentheses is supposed to be multiplied by every term in the parentheses, not just the first one. 5(x + 3) is equal to 5x + 15, not 5x + 3.
The rules for switching between decimals and percents can be easily confused. Keep in mind that moving a decimal two places to the right is multiplying by 100 and moving the decimal two places to the left is dividing by 100. Dropping a percent symbol is multiplying by 100 because doing so undoes dividing by 100, and writing a percent symbol is dividing by 100 because a percent symbol means “hundredths,” or “divided by 100.”
For statistics and probability questions, be careful about confusing mean, median, and mode. People often forget that the median of a set of data can be found only when the numbers are in order. When using scientific notation, be careful about the direction in which you move decimals. Numbers resulting from wrong decimal directions may be in the choices.
Sample questions
Which of the following has the same value as 35.937 percent?
A. 3,593.7
B. 3.5937
C. 0.35937
D. 35,937
E. 0.035937The correct answer is Choice (C). To convert a percent to a decimal number, drop the percent symbol, which can be % or the word “percent,” and move the decimal two places to the left. Choice (A) results from dropping the percent symbol and moving the decimal two places to the right. The other choices result from moving the decimal points something other than two places to the right or left. The main lesson here is that Choice (A) can be reached through a very common mistake in converting percents to decimals. You want to avoid such wrong choices. They’re lurking, so be ready.
45 17 90 28 17What is the median of the preceding set of data?
A. 28
B. 90
C. 17
D. 39.4
E. 45The correct answer is Choice (A). When the numbers are in order, the middle number is 28. It is therefore the median. Interestingly, Choice (A) also happens to be the range of the set of data. Hopefully, you didn’t reach the correct answer because you mistook median for range. Sometimes mistakes lead to the right answers, but we don’t advise counting on that method. Choice (B) is the middle number in the set of data as it is presented, but not when the data is in order. Choice (C) is the mode and the lowest number. Choice (D) is the mean. Choice (E) is just one of the numbers in the set of data.