Fast-track Addition up to 20 (Primary 1 Interviews): Master carrying with finger addition and tackle preschool math interview questions! 🧮🎓

Published : 07/10/2026

When preparing for Primary One interviews, many parents hope their children can quickly master addition within 20.

For example:

👉 8 + 8 = ?

👉 9 + 6 = ?

👉 7 + 5 = ?

If children can answer quickly, that’s certainly a good thing.

However, when preparing for Primary One interviews, there’s one more thing parents should pay attention to:

« Does your child really understand addition, or have they simply memorised the answers? »

In addition to straightforward addition questions, interviewers may also change the questions slightly to assess a child’s number sense, logic and understanding.

Here’s a simple way to help children grasp the basics of addition within 20.

Table of Contents

✋ Step 1: Use both hands to represent 0–10

We can start by turning fingers into a “number tool” that’s easy for children to understand.

One hand can represent 0–10

- 👊 Fist = 10

- ☝️ Index finger = 1

- ✌️ Index finger + middle finger = 2

- 🤟 Index + middle + ring fingers = 3

- 🖐️ Four fingers = 4

- 👍 Thumb = 5

- 👍☝️ Thumb + index finger = 6

- 👍✌️ Thumb + index finger + middle finger = 7

- 👍🤟 Thumb + index finger + middle finger + ring finger = 8

- 🖐️ Five fingers = 9

🧮 How do you work out 8 + 8? (One number + another number | Carrying addition)

For example, if the interviewer asks:

8 + 8 = ?

Children can start by using both hands to show 8.

Left hand: 5 + 3 = 8

Right hand: 5 + 3 = 8

This is where the “make ten” strategy comes in.

How much do you need to add to 8 to make 10?

The answer is 2.

So:

8 + 2 = 10

Subtract 2 from 8 on the left hand, leaving:

8 - 2 = 6

Therefore:

8 + 8

= 10 + 6

= 16

💡 The point of this method isn’t just to help children “work out 16,” but to help them start understanding:

«8 can be split into 2 + 6, and 2 can help make 10 with the other 8.»

This is the important early maths concept of “making ten.”

2. 🔢 How else can you work out 18 + 8? (Two addends + one addend | Carrying addition)

Once children have mastered addition within 20, they can gradually move on to adding a one-digit number to a two-digit number.

For example:

18 + 8 = ?

18 is:

10 + 8

First, we keep “10” in mind.

Then calculate:

8 + 8 = 16

Then add back the 10 they started with:

10 + 16 = 26

So:

18 + 8 = 26

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REPORT: Helping students observe and discover the relationship between game rules and winning strategies

3. 🔢 What about 18 + 18? (Two-digit + two-digit | Addition with carrying)

Once children have mastered the methods above, they can take on a further challenge:

18 + 18 = ?

18 can be split into:

10 + 8

Two 18s make:

10 + 8 + 10 + 8

First, keep both 10s in mind:

10 + 10 = 20

Then calculate:

8 + 8 = 16

Finally:

20 + 16 = 36

So:

18 + 18 = 36 🎉

At this stage, children are moving beyond simply counting on their fingers and beginning to understand the relationship between the tens and ones digits.

4. 🎓 Primary One Interviews: The Biggest Mistake Is When Children Only Know How to “Memorise Answers”

When preparing for Primary 1 interviews, many parents want their child to quickly memorise:

1+1, 2+2, 5+3, 8+8……

This kind of practice can help children calculate faster.

But proper preparation for Primary 1 interviews goes beyond simply “memorising answers.”

Because what if the interviewer asks:

8 + 8 = ?

The child answers:

16!

No problem.

But what if the teacher suddenly asks it another way:

❓ + 2 = 9

Would your child know the answer?

The answer is:

At this point, the teacher isn’t just checking whether children have memorised “7+2=9”.

Instead:

« Do children really understand the relationships between numbers?»

Olympiad Maths Games Class（ English Olympiad Maths ）

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Our introductory maths problem-solving course is designed for students who are ready to challenge themselves. A series of challenging Mathematical Olympiad-style problems helps students develop their analytical, problem-solving and logical reasoning skills.
Combine different types of mathematical concepts
Applying maths to everyday life

5. 🐸 Primary 1 interview math questions might also be asked like this!

For example:

“Froggy jumps forward 3 steps, hops 2 steps, then takes 1 step. Where does it end up?”

If they’ve only memorised addition facts, children may not understand the question straight away.

But if children know:

3 + 2 + 1 = 6

you can understand:

🐸 Jump = 3

🐸 Hop = 2

🐸 Step = 1

In total:

3 + 2 + 1 = 6

Froggy has moved forward 6 steps altogether.

This type of question tests whether children can connect a real-life situation → quantity → addition.

6. ⏱️ How can you practise the “120-second countdown”?

If you’d like your child to respond more quickly to math questions in Primary 1 interviews, you can add some simple countdown and mental math practice.

For example:

20, 19, 18, 17……

Then gradually increase the difficulty:

20, 18, 16, 14……

Or:

15, 14, 13, 12……

These exercises help children gradually develop a feel for number order and the distance between numbers.

The goal isn’t simply to be “fast,” but to help children gradually develop their own number sense (Number Sense).

7. What is mathematics? What is arithmetic?

Math isn’t just addition, subtraction, multiplication and division. Math is a science. Clearly, neither abacus mental arithmetic nor Kumon is a science! That’s why these are called arithmetic, not mathematics.

If you want to know what mathematics really is, you can read a book called A Mathematician’s Lament.

P.S. Using Montessori math materials is real mathematics. Math Olympiad is real mathematics too.

Reference: Curious Mum

8. ❤️ Addition up to 20 is just the beginning, not the end

PARENT TIP: Math games spark children’s interest in learning and make addition and subtraction easy. So, if you’re simply hoping for your child to:

«“ Help your child learn addition within 20 quickly to prepare for Primary One interviews.”»

So, learning to make ten, break numbers apart and count on your fingers can be a great way to get started.

But if you want your child to build a solid understanding of maths, it’s important to take things a step further:

✅ Number sequences

✅ Understanding quantity

✅ The relationship between addition and subtraction

✅ Number bonds and breaking numbers apart

✅ Make Ten

✅ Tens and ones

✅ Mental arithmetic

✅ Logical reasoning

✅ Real-life word problems

✅ Working backwards from the answer

Because the ideal preparation for Primary One interviews isn’t about having children memorise a large number of answers.

Even if the interviewer:

Change the question, ask it another way, add an extra step, or even turn it around,

Children can still work out the answer on their own.🧠✨

👉 If your child just needs to quickly master addition up to 20, start with this simple finger-counting and making-ten method.

👉 If you’d like your child to develop a stronger understanding of maths and confidently tackle variations on questions from interviewers, they should further develop their number sense, logic and mental maths skills.

Primary One interviews don’t just test whether a child “can do sums”; more importantly, they look at whether the child knows how to “think mathematically.” 🎓🧮

Fast-track Addition up to 20 (Primary 1 Interviews): Master carrying with finger addition and tackle preschool math interview questions! 🧮🎓

✋ Step 1: Use both hands to represent 0–10

🧮 How do you work out 8 + 8? (One number + another number | Carrying addition)

2. 🔢 How else can you work out 18 + 8? (Two addends + one addend | Carrying addition)

Maths Games Class ( Active Math Player )

3. 🔢 What about 18 + 18? (Two-digit + two-digit | Addition with carrying)

4. 🎓 Primary One Interviews: The Biggest Mistake Is When Children Only Know How to “Memorise Answers”

Olympiad Maths Games Class（ English Olympiad Maths ）

5. 🐸 Primary 1 interview math questions might also be asked like this!

6. ⏱️ How can you practise the “120-second countdown”?

7. What is mathematics? What is arithmetic?

8. ❤️ Addition up to 20 is just the beginning, not the end

Primary One interviews don’t just test whether a child “can do sums”; more importantly, they look at whether the child knows how to “think mathematically.” 🎓🧮

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