Welcome to the World of Subtraction!
Hello everyone! Today, we are going to learn about a very important friend in math: "subtraction."
Subtraction is a super handy tool we use when things disappear or when we want to compare quantities to see which is larger. It comes in very handy when you’re sharing snacks or comparing scores in a game.
It might feel a little tricky at first, but don't worry. If we take it one step at a time, you’ll definitely master it!
1. When do we use subtraction?
There are mainly two ways to use subtraction. Let's start by imagining the situations where we use it.
① How many are left? (Finding the remainder)
We use this when we want to find out how many are left after some have been taken away or have disappeared.
Example: There were 5 pigeons in the park. 2 flew away. How many are left?
Whenever you hear words like "gone away," "eaten," or "given away," it's time for subtraction!
② What is the difference? (Finding the difference)
We use this when we compare two things to see how many more (or fewer) one has than the other.
Example: There are 5 red marbles and 3 blue marbles. How many more red marbles are there?
When you are asked, "Which is more?" or "What is the difference?", subtraction is the way to solve it.
【Tip】
Whenever you see the phrases "How many are left?" or "What is the difference?", try asking yourself, "Is this a subtraction problem?"
2. Let's write subtraction equations
In math, we use numbers and symbols to express words briefly. The subtraction symbol we use is "\(-\)".
How to write equations and answers
If you want to write "take 2 away from 5" as an equation, it looks like this:
\(5 - 2 = 3\)
How to read it: 5 minus 2 equals 3
Symbol names:
\(-\) : This is called a "minus sign." It is the mark for subtraction.
\(=\) : This is the "equals sign." It shows that the number on the right is the answer.
3. Tips for subtraction
Here are some methods to help you calculate more smoothly.
① Use your fingers or blocks
When it's hard to solve just in your head, use your fingers or blocks.
1. First, hold up 5 fingers.
2. Fold down 2 fingers.
3. Count the remaining fingers, and you get 3! That is your answer.
② Remember the pairs that make "10"
If you memorize the pairs that make 10, like "10 is 3 and 7" or "10 is 4 and 6," subtraction becomes much easier.
Example: \(10 - 4 = 6\) (Because 10 is made of 4 and 6!)
【Fun Fact】
Subtraction is actually the "reverse" of addition. You can check if \(5 - 2 = 3\) is correct by seeing if \(3 + 2 = 5\) is true!
4. Common mistakes and things to watch out for
Knowing common pitfalls in advance will help you avoid mistakes.
× Don't mix up the order of the numbers
In subtraction, we basically subtract the "smaller number" from the "larger number."
You can calculate \(5 - 2\), but in first-grade math, you can't calculate \(2 - 5\). When writing an equation, always write the total amount (the larger number) first.
× Watch out for subtraction with "0"
\(5 - 0 = 5\)
When you subtract nothing, the number doesn't change. On the other hand,
\(5 - 5 = 0\)
If you subtract the same numbers, the answer is always 0. Just imagine eating a piece of cheese until it’s all gone!
5. Summary of this chapter
Finally, let's review the important points!
・Use subtraction for "How many are left?" or "What is the difference?"
・Use the symbol "\(-\)" and read it as "minus."
・Write the equation in the order of "larger number \(-\) smaller number."
・It's easier to practice by using your fingers or blocks to see the math in action!
Once you get the hang of subtraction, math will become more and more fun.
It's okay to start slowly. Practice a little bit every day, and get to know your numbers better. I'm rooting for you!