What is mental multiplication?

It is multiplying numbers in your head by splitting a number into easy parts — usually tens and ones — multiplying each part separately, then adding the results. For example, 23 × 6 = (20 × 6) + (3 × 6) = 138.

How do you multiply a two-digit number by a single digit in your head?

Break the two-digit number into its tens and ones, multiply each piece by the single digit, then add the two answers. For 24 × 5: 20 × 5 = 100, 4 × 5 = 20, so 24 × 5 = 120.

What is the quick trick for multiplying by 4?

Double the number, then double it again. For 15 × 4, double 15 to get 30, then double 30 to get 60. Doubling twice is easier than multiplying by 4 directly.

Why does multiplying by 10 or 100 just add zeros?

Multiplying by 10 shifts every digit up one place value, so a single zero is added on the end; multiplying by 100 shifts two places and adds two zeros. The digits themselves stay the same — 7 × 100 = 700.

What age or level is mental multiplication suitable for?

It suits Singapore primary learners around P2 to P4 (roughly ages 7–10) who already know their basic times tables, though older children can use it to speed up and check their work.

Multiply Big Numbers In Your Head

Math Interactive lesson Free to play

Mental multiplication is the skill of multiplying numbers in your head — without paper, a calculator, or column working — by breaking each number into friendlier parts. The core idea is place value: a two-digit number like 56 is really 50 + 6 (tens + ones). To multiply, you split the bigger number into its tens and ones, multiply each piece on its own, then add the pieces back together. For example, 23 × 6 becomes (20 × 6) + (3 × 6) = 120 + 18 = 138.

It matters because fast, confident mental maths underpins everyday tasks — working out totals while shopping, splitting a bill, estimating quantities — and frees up thinking time during school problem sums and exams. In the Singapore primary syllabus it strengthens number sense, which makes later topics like long multiplication and word problems feel easier.

Learners pick up two handy shortcuts along the way: multiplying by 10 or 100 just adds zeros (the digits stay the same), and multiplying by 4 is the same as doubling twice. Combined with the break-apart method, these turn 'big' multiplications into a few easy steps.

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A superpower for your brain

MENTAL MATH Multiply Big Numbers In Your Head 🧠✨ You don't need paper to multiply big numbers. You just need one clever idea: break the number into smaller, friendly pieces. 23 × 6 = 138 By the end, this will feel easy — promise! Tap Next to learn the trick. 👉
Break it apart

THE BIG IDEA Every number is tens + ones A two-digit number is really two friendly pieces hiding together. Look: 56 50 (tens) 6 (ones) 56 = 50 + 6 Your turn 🎯 Which one shows 56 broken into tens and ones? 5 + 6 50 + 6 56 + 10
The magic of zeros

SHORTCUT #1 Multiply by 10 or 100 fast When you multiply by 10, just add one zero. By 100? Add two zeros. The digits don't change! 7× 10 →70 7× 100 →700 Quick check ⚡ What is 8 × 10? 18 80 800 Tip: 8 grows a tail of one zero → 80.
Put the pieces together

THE FULL METHOD 23 × 6, step by step Break 23 into 20 and 3. Multiply each by 6, then add. Tap each card to reveal it! 👇 Tap: 20 × 6 = ? Tap: 3 × 6 = ? 120 + 18 = ? So what is 23 × 6? 128 138 148 Reveal both cards first, then add 120 + 18.
The doubling trick

SHORTCUT #2 ×4 = double, then double again Multiplying by 4 feels hard. But doubling twice is easy! Watch 15 × 4: 15 double → ? double → ? ▶ Double it! 15 → 30 → 60. So 15 × 4 = 60. Easy!
You try it!

YOUR CHALLENGE Solve it in your head 🧠 Break 24 into 20 + 4, multiply each by 5, then add. 20 × 5 = 100 4 × 5 = 20 24 × 5 = ? Check ✓ Add the two pink pieces: 100 + 20.
You did it!

RECAP You're a mental-math star! 🌟 🎉🧠🎈 Break apart the big number into tens + ones. Multiply each piece on its own (the easy parts). Add the pieces back together. Zeros shortcut: ×10 adds one zero, ×100 adds two. ×4 trick: double, then double again. Now try it on a number you see today — a price, a page number, anything. Your brain is the calculator! 💪

Frequently asked questions

What is mental multiplication?: It is multiplying numbers in your head by splitting a number into easy parts — usually tens and ones — multiplying each part separately, then adding the results. For example, 23 × 6 = (20 × 6) + (3 × 6) = 138.
How do you multiply a two-digit number by a single digit in your head?: Break the two-digit number into its tens and ones, multiply each piece by the single digit, then add the two answers. For 24 × 5: 20 × 5 = 100, 4 × 5 = 20, so 24 × 5 = 120.
What is the quick trick for multiplying by 4?: Double the number, then double it again. For 15 × 4, double 15 to get 30, then double 30 to get 60. Doubling twice is easier than multiplying by 4 directly.
Why does multiplying by 10 or 100 just add zeros?: Multiplying by 10 shifts every digit up one place value, so a single zero is added on the end; multiplying by 100 shifts two places and adds two zeros. The digits themselves stay the same — 7 × 100 = 700.
What age or level is mental multiplication suitable for?: It suits Singapore primary learners around P2 to P4 (roughly ages 7–10) who already know their basic times tables, though older children can use it to speed up and check their work.

Multiply Big Numbers In Your Head

What this Spark covers

Frequently asked questions

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