TASC Math Exam: Comparing Fractions, Decimals, and Percentages - dummies

TASC Math Exam: Comparing Fractions, Decimals, and Percentages

By Stuart Donnelly

Numbers come in all shapes, sizes, and forms, such as fractions, decimals, and percentages. When a TASC Math question asks you to compare numbers or put a set of numbers in a certain order, it’s easiest to do when they’re all in the same form.

  • Converting fractions to decimals. To convert a fraction to a decimal, divide the numerator by the denominator. The quotient could result in a terminating, repeating, or non-terminating, non-repeating decimal.

    To represent repeating decimals, put a bar over the digits that repeat.


  • Converting decimals to fractions. If the decimal is terminating, meaning it ends, you put the given digits over a power of 10. If there are two digits, you put them over 102 and then simplify if possible. Check out this example:


    You can always check your work by dividing numerator by denominator to make sure you get the same decimal you started with. Here’s another conversion example, this one with three digits:


    If the decimal is repeating, put the given repeating digits over 9s (depends on the number of digits that repeat). If there’s one digit that repeats, then it goes over one 9; if there are two digits that repeat, they go over two 9s, so 99. Then simplify if possible. For example:


    Here’s another example:


  • Converting percentages to decimals. To convert a percentage to a decimal, you must consider how you got that percentage in the first place. Percentage literally means per 100, so to go from a percent to a decimal, you move the decimal two places to the left. Mathematically this means you’re dividing by 100. Take at look at these examples:


Practice questions

  1. Which of the following is listed in ascending order?


  2. Which of the following is in descending order?


Answers and explanations

  1. The correct answer is Choice (A).

    Comparing numbers in different forms can be difficult, so you want to rewrite them all into the same form (usually decimals is the easiest).


    .6 is already a decimal,


    and 350% = 3.5. Now that they’re all in decimal form, you need to remember what ascending means: smallest to largest. This means the order should be


    Substituting back in the original values, you get:


    which is Choice (A).

  2. The correct answer is Choice (D).

    First rewrite each of the numbers into the same form (decimal form is probably the easiest).


    Now you can order them in descending order, which means from largest to smallest: 2.64, .7, .05, .03 and then substitute your original numbers back in:


    thus Choice (D) is correct.