Be a Maths Detective: Which Operation Do You Need? (Addition or Subtraction)

Hello Super Problem Solvers! Every word problem is like a little maths mystery waiting to be solved. Before you can find the answer, the most important first step is to figure out what kind of maths tool, or operation, you need to use. Are we putting things together (adding)? Or are we taking things away or finding a difference (subtracting)? Let’s learn how to look for clues!

Reading the Story: What’s Happening in the Problem?

The first thing a good maths detective does is read the word problem carefully and try to understand the “story.” Ask yourself:

• Are groups being joined together to make a bigger group?
• Is something being taken away, or are we finding out how much is left?
• Are we comparing two amounts to find the difference between them?
• Are we trying to find a missing part when we know the total and one part?

Understanding the story helps you choose the right operation!

Clue Words: Your Secret Decoder Ring!

Word problems often have “clue words” that can help you decide whether to add or subtract. Think of these as secret messages!

Clue Words That Often Mean ADDITION (+): When things are being put together, increased, or you’re finding a total.

• sum (What is the sum of 15 and 20?)
• total (What is the total number of apples?)
• altogether (How many birds are there altogether?)
• in all (How many sweets in all?)
• combined (What is their combined height?)
• plus (What is 7 plus 5?)
• add (If you add these numbers…)
• increase by (The price increased by £10.)
• more / more than (If asking for a new, larger amount e.g., “What is 5 more than 12?”)

Example (Addition): “Lila has 112 stickers. Tom gives her 35 more stickers. What is the total number of stickers Lila has now?” The words “more” and “total” suggest we need to ADD.

Clue Words That Often Mean SUBTRACTION (−): When things are being taken away, reduced, or you’re finding out how much is left or the difference.

• difference (What is the difference between 50 and 20?)
• how many left (How many cookies are left?)
• take away (If you take away 15…)
• minus (What is 100 minus 40?)
• fewer / fewer than (She has 12 fewer cats than dogs.)
• less / less than (He has £5 less than his sister. / What is 7 less than 19?)
• decrease by (The temperature decreased by 5 degrees.)
• how many more… than (When comparing two numbers, e.g., “How many more apples does Ben have than Mia?”)
• remain (How many sweets remain?)

Example (Subtraction): “Max had 245 marbles. He lost 23 of them. How many marbles does he have left?” The words “lost” and “left” suggest we need to SUBTRACT.

Important Detective Note: Sometimes a clue word can be tricky! Always read the whole problem to understand the story. For example, “more than” can sometimes be part of a subtraction problem if you’re comparing.

Crack the Case: Which Operation is It? (18 Mysteries)

Ready to use your detective skills? For each word problem below, your main job is to decide: Do I need to add, or do I need to subtract? You can also try to solve them if you like, but the big challenge here is choosing the correct operation!

(Your web app with the 18 questions will go here. Questions should present word problems and primarily ask the child to identify the correct operation(s) needed, perhaps by clicking an add or subtract symbol, or choosing from options.)

Why is Identifying the Operation So Important?

• It’s the First Step to the Right Answer: If you choose the wrong operation, you can’t solve the problem correctly!
• Shows You Understand the Problem: It proves you’ve read the “maths story” and know what’s happening.
• Builds Problem-Solving Confidence: Knowing what to do is a huge part of feeling good about maths.
• Helps with Harder Problems Later: As problems get more complicated (like two-step problems!), knowing how to identify each operation needed is super important.

Tips for Grown-Ups: Helping Children Choose the Right Operation

Helping children identify the correct operation in a word problem involves developing their reading comprehension and their understanding of what addition and subtraction actually do.

• Focus on the Action: Ask, “What is happening to the numbers in this story? Are they being joined? Is something being taken away? Are we comparing?”
• Discuss Keywords, But With Caution: Teach common keywords (like “total” for addition, “left” for subtraction) but also explain that the overall context is most important, as some keywords can be ambiguous.
• Visualise the Problem: Encourage drawing a picture, using a bar model, or acting out the problem with objects. This can make the necessary operation much clearer.
• “What kind of answer are we expecting?”: Ask if they expect the answer to be bigger or smaller than the numbers in the problem. This can often point to addition (bigger) or subtraction (smaller).
• Start Simple: Use very simple one-step problems with clear language and obvious operations before moving to more complex phrasing.
• Talk About It: After they choose an operation, ask “Why did you choose addition/subtraction for this problem?” Hearing their reasoning can help identify any misunderstandings.