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Become a math detective by finding clues in word problems to decide whether to add or subtract.
Imagine you are a detective at a birthday party. If 20 balloons are blown up but 5 of them pop, how do you find out exactly how many are left without counting them one by one?
When we solve a math story, we look for clue words. If a story asks how many things there are altogether, in total, or in all, it is usually an addition mystery! Addition is like putting two groups of toys into one big box. We use the plus sign to show we are joining groups together. Think of it as building a taller tower out of blocks! When we add, our answer gets bigger because we are combining things.
Leo has red marbles. He finds blue marbles. How many does he have altogether?
1. Find the numbers: and . 2. Find the clue: altogether means we need to add (). 3. Write the code: . 4. Leo has marbles in his collection!
Quick Check
If a story asks for the 'total' number of cupcakes, should you add or subtract?
Answer
You should add.
Sometimes things go away in a story. If you see words like left, remain, fewer, or take away, you have a subtraction mystery! Subtraction is like eating some cookies from a jar; you want to know what is still there. We use the minus sign to show we are taking something away from a group. It helps us find the difference between two numbers. When we subtract, our answer is usually smaller than the number we started with.
Sarah baked cookies. Her friends ate of them. How many cookies are left?
1. Find the numbers: and . 2. Find the clue: left means we need to subtract (). 3. Write the code: . 4. Solve: , then . 5. There are cookies left!
Quick Check
Which word is a clue to subtract: 'sum' or 'fewer'?
Answer
The word 'fewer' is a clue to subtract.
To be a master detective, you must turn the story into a number sentence. This is a short way to write the math mystery using numbers and symbols. Always check if your answer makes sense. If you add, your total should be bigger than the numbers you started with. If you subtract, your answer should be smaller! This is called 'checking your work' to make sure your detective skills are sharp and your answer is correct.
A toy store had puzzles. They sold puzzles in the morning. How many puzzles does the store have now?
1. Identify the numbers: and . 2. The action 'sold' means the puzzles are gone, so we subtract (). 3. Write the code: . 4. Solve: , then . 5. The store has puzzles remaining.
Which word tells you that you should probably add?
There are birds on a fence. birds fly away. How many birds are left?
If a math story uses the word 'sum,' you should subtract the numbers.
Review Tomorrow
In 24 hours, try to remember three clue words for addition and three clue words for subtraction.
Practice Activity
Next time you go to the store, look at two items and try to find their 'total' price by adding them together!