Dive into Fractions: How to Solve Addition and Subtraction Word Problems

TL;DR: Fraction word problems are really just fraction addition or subtraction wrapped in a sentence or two. Read the situation carefully, write down the fractions, decide whether you're adding or taking away, find a common denominator, then solve. Last step (and the one most people skip): glance back at the original question and make sure your answer actually fits what was asked. Fractions don't lie, but a careless reread can save you from answering the wrong question.

Key takeaways:

  • Read the problem twice, once for the story, once for the numbers.
  • Underline or write down the fractions you'll work with.
  • Decide whether you're adding (combining), subtracting (finding what's left), or comparing.
  • Find a common denominator before adding or subtracting.
  • Re-read the question to make sure your numerical answer actually answers it.

Welcome back, budding mathematicians! Today, we’ll explore a new exciting topic: word problems involving addition and subtraction of fractions. Don’t let the term ‘word problems’ intimidate you. With some simple steps, you can tackle these like a pro.

Dive into Fractions: How to Solve Addition and Subtraction Word Problems

Adding and Subtracting Fractions: A Refresher

Adding and subtracting fractions involves a little more than adding and subtracting whole numbers, but the concept is pretty straightforward. It revolves around the idea of finding a common denominator, which is a shared multiple of the denominators of the fractions involved.

Step-by-Step Guide: Adding and Subtracting Fractions in Word Problems

Step 1: Understand the Problem

Read the problem carefully. Understand what is being asked and identify the fractions you will need to add or subtract.

Step 2: Find the Common Denominator

This is perhaps the trickiest part. The denominators of the fractions must be the same before you can add or subtract them. To find the common denominator, look for the least common multiple (LCM) of the denominators.

Step 3: Adjust the Fractions

Once you have the common denominator, adjust the fractions by multiplying the numerator and denominator by the same number so that the denominator matches the common denominator.

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Step 4: Add or Subtract

Now, add or subtract the numerators of the fractions. The denominator remains the same.

Step 5: Simplify the Answer

After performing the operation, simplify your answer if possible. This may involve reducing the fraction to its lowest term.

Step 6: Write the Answer

Finally, write down your answer, making sure it correctly answers the question asked in the word problem.

Now, let’s see this process in action:

Ella has \(\frac{2}{3}\) of a chocolate bar left, and her friend Mia has \(\frac{1}{2}\) of a chocolate bar left. How much chocolate do they have together?

  1. Understand the problem: We need to add \(\frac{2}{3}\) and \(\frac{1}{2}\).
  2. Find the common denominator: The LCM of \(3\) and \(2\) is \(6\).
  3. Adjust the fractions: \(\frac{2}{3}\) becomes \(\frac{4}{6}\), and \(\frac{1}{2}\) becomes \(\frac{3}{6}\).
  4. Add the fractions: \(\frac{4}{6} + \frac{3}{6} = \frac{7}{6}\).
  5. Simplify the answer: \(\frac{7}{6}\) can be written as \(1\frac{1}{6}\).
  6. Write the answer: Ella and Mia have \(1\frac{1}{6}\) chocolate bars together.

Remember, the key to mastering word problems involving fractions is practice. So, roll up your sleeves and get started!

Recommended EffortlessMath Books

For a complete fractions workbook that drills word problems alongside core fraction skills, the Grade 5 Common Core Math for Beginners (resource currently unavailable) walks through every grade-5 topic with worked examples. For state-test prep with word problems in test format, the Grade 5 FSA Math for Beginners (resource currently unavailable) covers the same skills in FSA question style.

Frequently Asked Questions

How do you solve adding and subtracting fractions word problems?

Read the story, write down the fractions, decide whether the question combines amounts or takes one away, then find a common denominator and calculate. For example, Lena walks 2/3 mile to the park and then 1/4 mile to the store. Using twelfths, 8/12 + 3/12 = 11/12, so she walks 11/12 of a mile in all.

How do you know whether to add or subtract in a fraction word problem?

Look at what the question asks for. Words such as in all, total, together and combined usually signal addition. Words such as left, remaining, how much more and difference usually signal subtraction. If a recipe uses 3/4 cup of milk and you have 1 cup, asking how much is left means 1 − 3/4 = 1/4 cup.

How do you solve fraction word problems with unlike denominators?

Rewrite both fractions with the least common denominator before you add or subtract. Say a jug holds 5/6 liter of juice and you pour out 3/8 liter. The LCD of 6 and 8 is 24, so 5/6 = 20/24 and 3/8 = 9/24. Then 20/24 − 9/24 = 11/24, which means 11/24 liter of juice is still in the jug.

How do you subtract mixed numbers in a word problem?

Change each mixed number to an improper fraction, use a common denominator, subtract, then convert back. A rope is 3 1/2 meters long and 1 3/4 meters is cut off. 3 1/2 = 7/2 = 14/4 and 1 3/4 = 7/4, so 14/4 − 7/4 = 7/4. That simplifies to 1 3/4 meters of rope remaining.

What do you do with extra information in a word problem?

Ignore any detail that does not change the calculation. In a problem like Ava painted 2/5 of a fence on Saturday morning with her blue brush and 1/5 on Sunday, the day and the brush color do not matter. Only the fractions 2/5 and 1/5 count, and together they give 3/5 of the fence painted.

What grade learns adding and subtracting fraction word problems?

Under the Common Core standards, students begin solving fraction addition and subtraction word problems with like denominators in 4th grade. In 5th grade they move on to unlike denominators and mixed numbers, and 6th graders use these skills inside longer, multi-step problems. Many state tests in grades 4 to 6 include at least a few of these questions.

Related EffortlessMath Lessons

If a topic on this page feels rusty, these short lessons go deeper:

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