If fractions are where math lost you in school, you’re in good company. And you’re not starting from zero.
You already know that half off, 50% off and paying 0.5 of the price all mean the same thing at the register. That’s this whole topic: three ways to write one amount, used mostly on prices, tips and tax.
The catch? The test switches between the three forms without warning, and a percent question often has two steps where you expect one. The answer you get by stopping halfway is usually sitting right there in the choices.
On this page you’ll get:
- 25 practice questions (scroll up), new ones every time
- How to switch between fractions, decimals and percents
- Percent of a number, percent change and sale prices
- The traps hidden in percent questions
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 these questions look like, in dollars and cents
Most questions here are about money. You’ll see a diner bill with tax and tip, a jacket on sale, rent going up, or a savings account left alone for three years. A few are plain sums, like 3/4 + 1/8, or putting four numbers in order on a number line.
Switching forms is the skill under all of it. Think of a quarter: it’s 1/4 of a dollar, $0.25, or 25% of a dollar. Same coin, three labels.
Here’s how to switch. To turn a fraction into a decimal, divide the top by the bottom: 3 ÷ 4 = 0.75. To turn a decimal into a percent, move the point two places to the right, so 0.75 becomes 75%.
Going back is the same move in reverse. To use 20% in a calculation, move the point two places left and it becomes 0.20.
Percent of a number means “this many out of every 100”. For 20% off a $45 jacket, multiply: $45 × 0.20 = $9 off. The sale price is $45 − $9 = $36. That second step, taking the $9 off, is the one people skip.
Percent change compares the change with where you started. Picture a $40 shirt marked down to $30. It dropped $10, and $10 out of the original $40 is 25%.
Rent works the same way. If it goes from $800 to $900, the $100 rise is compared with the $800 you used to pay, so it’s a 12.5% increase.
The official test guide lists the money settings it uses: interest, tax, markup and markdown, tips, commission and percent change. Most take two steps: find the percent, then add it on or take it off.
The first five or so questions have no calculator, so small sums like 3/4 + 1/8 or 25% of 80 could show up there. After that you get the TI-30XS, which has a fraction key that simplifies answers and switches between fractions and decimals.
How many questions? There’s no official count per topic. This one shares about 25% of the test with number operations, ratios and exponents, so our estimate is four or five out of about 46.
The topics and area weights come from GED Testing Service’s official test guide. It doesn’t publish a question count per topic, so any count here is our estimate.
The 4 mistakes that cost the most points
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.
1Adding fractions straight across
1/2 + 1/3 isn’t 2/5. Picture one pizza cut in halves and another cut in thirds: the slices are different sizes, so you can’t just count them. Cut both into sixths first: 3/6 + 2/6 = 5/6. (And 2/5 is smaller than the 1/2 you started with, which can’t be right after adding.)
2Using a mixed number without converting it
Say a recipe needs 1 1/2 cups of flour and you’re making 2/3 of it. Turn 1 1/2 into 3/2 first, then multiply: 3/2 × 2/3 = 1 cup. Dividing by a fraction works like this too: flip it and multiply, so dividing by 3/4 means multiplying by 4/3.
3Taking the percent off as dollars
On a $45 jacket at 20% off, the choice of $25 comes from taking $20 off instead of 20%. Twenty percent of $45 is $9, so the jacket costs $36. Interest trips people the same way: in I = Prt, 5% goes in as 0.05. Change the percent to a decimal before you use it.
4Dividing by the new amount instead of the old one
Rent that goes from $800 to $900 has gone up 12.5%, because the $100 rise is compared with the $800 you started from. Dividing by $900 gives 11.1%, and that wrong answer will be a choice. Before you divide, ask yourself: what was it before?
One problem, worked out step by step
Simone orders dinner for a study group. The food comes to $46.00 before tax. Sales tax is 7%, and she leaves an 18% tip based on the cost before tax. What is the total amount she pays?
The working
- Find the sales tax
Tax is a percent of the pre-tax food cost. Turn 7% into a decimal by dividing by 100, then multiply.
$46.00 × 0.07 = $3.22 - Find the tip on the same base
The tip is figured on the food before tax, so it also uses $46.00 rather than the taxed amount. Taking 18% of $49.22 instead gives $8.86 and a wrong total.
$46.00 × 0.18 = $8.28 - Add the three amounts
The total is the food plus the tax plus the tip, every amount in dollars and cents.
$46.00 + $3.22 + $8.28 = $57.50 - Check with one multiplication
Tax and tip together are 7% + 18% = 25% of the bill, so the total should be 125% of $46.00, and it is.
$46.00 × 1.25 = $57.50
Answer: $57.50
How to get better at this, fast
- Learn a few conversions the way you know coins: 1/8 = 0.125, 3/8 = 0.375, 2/5 = 0.4, 5/8 = 0.625. Ordering questions get much quicker once everything is in one form.
- Before any percent problem, label three things: the whole, the percent and the part. Every percent question is part = whole × percent, turned around.
- Simple interest is on the formula sheet as I = Prt. Compound interest isn’t, so multiply the balance by (1 + rate) once for each year, rounding to the cent each time.
- Underline what the last sentence asks for: the discount or the sale price, the tip or the total, the interest or the new balance. The answer to the other one is usually a choice.
Frequently asked questions
Can I use a calculator for fractions on the GED math test?
Yes, after the first five or so questions. The TI-30XS has a fraction key that handles mixed numbers and simplifies answers. You’ll still do a little fraction work by hand at the start.
Is compound interest on the GED formula sheet?
No, only simple interest (I = Prt) is there. For compound interest, multiply by (1 + rate) one year at a time. Percent change isn’t on the sheet either: it’s the change divided by the original, times 100.
What kinds of percent problems does the GED ask?
The official test guide lists interest, tax, markup and markdown, tips, commission and percent change, usually as two-step problems. Each one starts with finding a percent of a number.
How many fraction and percent questions are on the GED math test?
There’s no published count for a single topic. Our estimate is four or five, based on the 25% of the test this topic shares with three others.
Keep going
The formula sheet, explained
Simple interest is on it and compound interest is not; here is what to do about both.
Ratios and proportions practice
A percent is a ratio out of 100, and proportions are the other way to solve most percent problems.
The GED calculator, explained
How the fraction key, the toggle key and the percent key work, and when you cannot use them.