Fractions, Decimals and Percents on the GED Math Test

Wrong answers here follow a pattern. Fractions get added straight across, so 1/2 + 1/3 becomes 2/5. A 20% discount gets subtracted as twenty dollars. A rent increase from $800 to $900 gets divided by the $900. The interest earned sits among the choices when the question asked for the balance. Each of those is a wrong answer our generator writes on purpose.

This topic belongs to "quantitative problem solving with rational numbers", which GED Testing Service weights at 25% of the test and which also covers number operations, ratios and exponents. That is eleven or twelve of about 46 questions for the whole group, and since percent problems have an indicator of their own, four or five questions here is our guess rather than an official count.

Skills in this set: Percent increase and decrease · Comparing fractions, decimals and percents · Adding and subtracting fractions with unlike denominators · Multiplying and dividing fractions and mixed numbers · Converting among fractions, decimals and percents · Finding a percent of a number · Finding what percent one number is of another · Finding the original price before a discount or markup · Simple interest with I = Prt · Compound interest · Percent increase and percent decrease · Sales tax and tip on a bill

What the test asks

Four indicators from the Assessment Guide for Educators apply. Q.1.a is putting fractions and decimals in order, including on a number line. Q.2.a is the arithmetic: adding, subtracting, multiplying and dividing fractions and decimals, mixed numbers included. Q.3.c is multi-step ratio problems, and a percent is a ratio out of 100. Q.3.d is two-step percent problems from everyday life, and the guide names the settings: interest, tax, markup and markdown, tips, commission and percent change.

The contexts are a diner bill with tax and tip, a used bike with a deposit, a savings account left alone for three years, a quiz with 17 of 20 correct. Drop-down items ask you to complete a sentence such as "a percent increase of ___", drag-and-drop items ask you to order values written in mixed forms, and fill-in-the-blank items want a typed number, cents included.

Expect fractions and simple percents in the opening no-calculator section, where the first five or so questions are what GED Testing Service calls mental math; 3/4 + 1/8 or 25% of 80 is the size of thing that fits. For the rest of the test the TI-30XS has a fraction key that returns answers in lowest terms, takes mixed numbers, and toggles between fraction and decimal form.

The mistakes this set is built to catch

Each wrong answer in the practice set is the result of one specific slip, and the explanation names it. These are the ones that come up most in this topic.

A worked example

How to practice it

1. Convert every fraction you meet to a decimal and back until the common ones are instant: 1/8 = 0.125, 3/8 = 0.375, 2/5 = 0.4, 5/8 = 0.625. Ordering questions get easy once everything is in one form, and the no-calculator section leaves you no other way to do them.
2. For any percent problem, label the whole, the percent and the part before you compute. Percent-of questions give the whole and the percent, what-percent questions give the part and the whole, and original-price questions hide the whole. The operation is always part = whole × percent, rearranged.
3. Simple interest is principal × rate × years, and it is on the formula sheet. Compound interest is not, so build it: multiply the balance by (1 + rate) once for every year, rounding to the cent each time, then subtract the principal only if the question asks for the interest alone.
4. Underline what the last sentence of a money question asks for: the interest or the balance, the discount or the sale price, the tip or the total. Our practice set puts the answer to the neighboring question among the choices on purpose.