  # 15 Tricks to boost your Primary student's Mental Maths skills Calculations are a necessity in daily life, and being able to perform them quickly and with accuracy can provide a major benefit for everyone.

For primary students, being able to do calculations in their head is not only beneficial for school work but also for other aspects of life. So, to help primary students with this skill, we have put together 15 tricks that they can use to speed up their ability to do calculations without having to use paper or calculators. With these tricks, students will be able to quickly come up with the answers they need to ace important exams like PSLE.

## Why is it important for primary students to do quick calculations in their heads?

It is critical for students to be able to quickly do calculations in their heads, as it helps them to better understand basic Maths concepts. By having the ability to rapidly process numerical information, students can more easily identify patterns and relationships between numbers, such as addition, subtraction, fractions, and percentages.

Why is this important?

Well, if you look at some of the toughest questions in previous years' PSLE exams (like the 2019 triangle and semi-circle questions), you'd know that many of them involve being able to identify patterns and relationships before identifying the formula that will help them solve the question.

Additionally, Mental Maths skills give students the confidence they need to tackle more complex Maths problems later in life.

Developing these skills early on puts kids ahead of the curve when it comes to higher-level mathematics. Mental Maths encourages creativity and problem-solving, leading students towards greater achievement in their studies.

## So, let's take a look at some of these Mental Maths tricks that all students need to know.

Tricks for Subtraction

Tricks for Multiplication

### Trick 1: Adding 10 or 100

Adding 10 or 100 to a number is a simple and easy trick that primary students can use. For example, if a student needs to add 10 to 25, they can simply add 1 to the tens place, making it 35. Similarly, to add 100 to 534, the student can add 1 to the hundreds place, making it 634.

### Trick 2: Doubles

One trick for doing quick calculations in your head is to use doubles. Doubles are simply two numbers that are the same when added together. For instance, 2+2 is a double (because they are the same number). If you double 2, the answer is 4. So 2+2=4.

To give you another example, let's say you need to add 5+5 together. Instead of adding each number individually, you can recognise that if you double 5, you get 10. So, 5+5=10!

This trick can work with other numbers as well. For example, if you need to add 6+6 together, you can recognise that 6 is a double of 3 (because 3+3=6). So, you simply need to double 3 to get the answer. That means 3+3=6!

Using doubles can be a quick and efficient way to do basic addition in your head, without having to count each number individually.

### Trick 3: Make 10

You can break apart a number to make 10.

Say for example you want to solve 7+9.

First, look at the number that's closer to 10. In this case, it is 9.

Now to make a 10, we need to add 1 to 9.

So, now if we need to break apart 7 in two parts, keeping one part as 1, what will be the other part?

If you answered 6, you are correct!

So, we know that 9+1=10.

Now, we need to add 6 that we calculated just now to 10, we get 16!

### Trick 4: Bridge through 10

Bridging through 10 is a trick that helps with addition problems that cross over the number 10.

For example, if a student needs to add 8+7, they can first add 2 to 8 to make it 10, and then add the remaining 5 to 10, making it 15.

### Trick 5: Left-to-right trick for bigger numbers

This trick involves breaking down larger numbers into smaller parts and adding them from left to right. It can be particularly useful when adding numbers that are many digits long, such as 345+267.

For example, let's add 345 and 267. First, we look at the hundreds place - that's the first number on the left. We add 3 and 2, which is 5. So the first part of our answer is 5.

Next, we look at the tens place - that's the second number from the left. We add 4 and 6, which is 10. But instead of writing down the 0 and carrying over the 1 to the next place, we add the 1 to the result we got from the hundreds place. So we add 1 to 5, which is 6. So now our answer is 65.

Finally, we look at the ones place - that's the last number on the right. We add 5 and 7, which is 12. But since we already added the 1 from the tens place, we don't need to carry anything over. So our final answer is 612.

See, it's like breaking a big problem into smaller pieces that are easier to solve!

### Trick 6: The splitting trick

If you want to take away a small number from a big number, you can split the big number into two parts. Then, you take the smaller number away from the bigger part of the big number.

For example, if we want to find the answer to 23-18, we can split 23 into 20 and 3.

Then, we take away 18 from 20 which gives us 2.

After that, we add the remaining 2 from the big number to the 3 we got before, which gives us 5.

So, 23 - 17 = 5.

### Trick 7: Rounding-up

This trick works best for subtracting numbers close together, for example, 28-21.

To solve this using the rounding-up trick:

- Determine which number is smaller and which is larger. In this case, 28 is the larger number and 21 is the smaller number.

- Round up the smaller number to the nearest multiple of 5 or 10. For our example, we round up 21 up to 25.

- Now, find the difference between the larger number and the rounded-up smaller number. Which is 28-25=3.

- Determine how much you need to subtract from the rounded-up smaller number to get back to the original number. In our example, subtract 4 from 25 to get back to 21.

- The result of the subtraction is 3 (that we got from 28-25)+4 (25-21)=7.

### Trick 8: Adding up to subtract

'Adding up to subtract' is a trick that helps with subtraction problems that involve subtracting larger numbers from smaller ones. For example, if a student needs to subtract 7 from 12, they can add 3 to 7, making it 10, and then subtract 10 from 12, making it 2.

### Trick 9: Subtracting by grouping

Subtracting by grouping is a trick that helps with subtraction problems that involve subtracting large numbers from other large numbers. For example, if a student needs to subtract 486 from 1000, they can solve it by following these steps:

1. Identify the two numbers that you need to subtract. Let's use the example of 1000 - 486.
2. Look at the smaller number (486 in this case) and break it up into groups of hundreds, tens, and ones. In this case, you would have 4 groups of 100, 8 groups of 10, and 6 ones. So, 486 can be written as 400 + 80 + 6.
3. Starting with the largest group (400), subtract it from the larger number (1000) and write the result underneath. In this case, 1000 - 400 = 600.
4. Move on to the next largest group (80) and subtract it from the previous result (600). Write this result underneath. In this case, 600 - 80 = 520.
5. Finally, subtract the last group (6) from the previous result (520). Write this result underneath. In this case, 520 - 6 = 514.
6. The final result is 514, so 1000 - 486 = 514.

### Trick 10: The complement method

The Complement Method can be especially useful for subtracting numbers that are close to a multiple of 10. Here's how you solve subtraction problems using this method:

Example: 54 - 8

1. Identify the number being subtracted: The number being subtracted is 8.

2. Find the complement of the number being subtracted: To find the complement of 8, we need to add a number to it that gives us the nearest multiple of 10. In this case, we add 2 to 8 to get 10. Therefore, the complement of 8 is 2.

3. Add the complement to the number you're subtracting from: Add the complement (2) to the number we're subtracting from (54):

54 + 2 = 56

4. Finally, subtract the original whole number (10) from the result (56) = 46.

So, the answer to the question 54-8 is 46.

### Trick 11: Doubling and Halving

This is a multiplication trick. To use this technique, you half one number and double the other.

Let's say we want to find the product of 36 and 12.

First, we'll halve the larger number, which is 36, to get 18.

Next, we'll double the smaller number, which is 12, to get 24.

Now, we have the simpler problem of finding 18 x 24.

We can simplify this further by applying the same trick again by halving 18 to get 9 and doubling 24 to get 48.

So, now we have to find 9 x 48, which is 432.

Therefore, the product of 36 and 12 is 432.

Adding groups is a trick that helps with multiplication problems that involve multiplying by multiples of 10. For example, if a student needs to multiply 6 by 30, they can first multiply 6 by 3, making it 18, and then add a zero to the end, making it 180.

### Trick13: Break it down

This technique works best when multiplying a one-digit number with a two-digit number. Let's understand how to do this using an example:

Let's say we want to multiply 8 by 14.

Step 1: Break up 14 into 10 and 4.

Step 2: Multiply 8 by 10.

8 x 10 = 80

Step 3: Multiply 8 by 4.

8 x 4 = 32

Step 4: Add the two results together.

80 + 32 = 112

Therefore, 8 x 14 = 112.

### Trick 14: The multiply by 9 trick

To quickly multiply a number by 9, hold out both hands with your fingers extended. The finger that corresponds to the number being multiplied is bent down. For example, to multiply 7 x 9, you would bend down the 7th finger from the left. The fingers on the left of the bent finger represent the tens digit, and the fingers on the right represent the ones digit. In this case, there are 6 fingers on the left of the bent finger and 3 fingers on the right, so the answer is 63.

### Trick 15: The 9s trick

This trick is based on the fact that the digits of the answer of any multiplication of a single-digit number and 9 will always add up to 9.

For example:

• 9 x 2 = 18 (1+8=9)
• 9 x 3 = 27 (2+7=9)
• 9 x 4 = 36 (3+6=9)
• and so on...
Let's understand how to use this information using an example. Let's say we want to multiply 23 by 9.
1. Take any two-digit number (for example, 23).
2. Subtract 1 from the first digit (2-1=1).
3. Subtract the result from 9 (9-1=8).
4. Put the result (8) in front of the original two-digit number (823).

So, 23 x 9 = 207.

This trick works because when you subtract 1 from the first digit and add that to the second digit, the sum is equal to 9. For example, in the case of 23, 2-1=1 and 1+3=4, which adds up to 9. Then, when you subtract the result from 9, you get the first digit of the answer, and the second digit is the original two-digit number.

Learning how to do quick calculations in their head is an important skill for primary students. These 15 tricks can help students improve their mental Maths skills and make calculations easier and faster.

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