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8 great Mental Math multiplication tricks to make you a Math whiz!

So, what is this Mental Math?

Mental math is a way to use only one tool, your brain, to quickly crunch numbers in your head. No calculators, no paper, no pen!

Most mental math is really a series of strategies – some very simple, some that need more practice to remember, but all quick, easy and a great workout for your brain🧠! Ready to give this a try?

Trick # 1 – Round Up or Down!

In school, we’ve always been taught by our teachers and parents to add and subtract numbers from right to left and always make sure to carry the one left. This works great when you have a paper and a pencil but my brain refuses to think right –> left, and guess what, I forgot to carry the 1 again!

When your brain needs to work this out quickly though, here’s an easy Mental Math trick: Round the numbers, up or down!

Rounding – Example 1:

  • You’re given: 796 + 812.
  • Step 1: Round these quickly to 800 and 800. 800 + 800 = 1600.
  • Step 2: 796 = 800 – 4; 812 = 800 + 12. Add these two together to get -4 + 12 = 8.
  • Step 3: 1600 + 8 = 1608.

As you can see, rounding makes the numbers more manageable and easier to solve..

Rounding – Example 2:

  • You’re given: 89 x 6.
  • Step 1: Round 89 quickly to 90 and 6. 90 x  6 = 540.
  • Step 2: We used an extra 6, so subtract that from the answer. 540 – 6 = 534

Trick # 2 – Break down and multiply in parts

This is an important, foundational thing that can help multiply and divide pretty quickly once you get the hang of it. Don’t reach for your calculator until you try this!

Example 1:

  • You’re given 3 x 68
  • Step 1: Break it down, shall we? 3 x 78 is the same as 3 x 60 + 3 x 8
  • Step 2: 3 x 60 + 3 x 8 = 180 + 24 = 204

Almost TOO easy, right? Let’s try a larger number then.

Example 2:

  • You’re given 7 x 328
  • Step 1: Break it down, shall we? 7 x 328 is the same as 7 x 300 + 7 x 20 + 7 x 8
  • Step 2: 7 x 300 + 7 x 20 + 7 x 8= 2100 + 140 + 56= 2240 + 56 = 2296

Again, easy, right?  Don’t chuck that calculator yet – we’ll use it for more complex things. But this is a great way to keep your mind active and focused.

Trick # 3 – Doubling a number

A skill that everyone should learn in Math is doubling. Let’s combine our skill we learnt above (break down and multiply in parts.

Example 1:

  • Given – 38 x 2 = 38 + 38
  • Break down – you know how! 30 + 30 + 8 + 8 = 60 + 16 = 76.

Too easy? Let’s try a harder one.

Example 2:

  • Given – 929 x 2 = 929 + 929
  • Break down – you know how! 900 + 900 + 20 + 20 + 9 + 9= 1800 + 40 + 18 = 1840 + 18 = 1858.

Got that? Hey, you’re getting good at this!

Trick # 4 – Four times a number

This is probably one of my most-used tricks!  You’ve mastered doubling now, right? Let’s extend that skill.

Four times a number = double a number + double a number, so basically double a number twice.

Example 1:

  • Given – 38 x 4 = 38 + 38 + 38 + 38
  • Break down part 1 – double it! 30 + 30 + 8 + 8 = 60 + 16 = 76.
  • Now double it again – 76 + 76 = 70 + 70 + 6 + 6 = 140 + 12 = 152.

A slightly harder one, now that you have the hang of this.

Example 2:

  • Given – 929 x 4 = 929 + 929 + 929 + 929
  • Break down part 1 – double it! 900 + 900 + 20 + 20 + 9 + 9= 1800 + 40 + 18 = 1840 + 18 = 1858.
  • Now repeat it to double again – 1858 + 1858 = 1800 + 1800 + 50 + 50 + 8 + 8 = 3600 + 100 + 16 = 3716

Yes? Well, you’re officially a genius!

Trick # 5 – Eight times a number

You’ve got this, haven’t you?  Multiply by 8 means doubling 3 times!

Example 1:

  • Given – 38 x 8 = 38 x 2 + 38 x 2 + 38 x 2 
  • Break down part 1 – double it! 30 + 30 + 8 + 8 = 60 + 16 = 76.
  • Break down part 2 – double it again to get 38 x 4 = 76 + 76 = 70 + 70 + 6 + 6 = 140 + 12 = 152.
  • And finally – double it again – 152 + 152 = 150 + 150 + 2 + 2 = 304.

Example 2:

  • Given – 929 x 9 = 929 x 2 + 929 x 2 + 929 x 2
  • Break down part 1 – double it! 900 + 900 + 20 + 20 + 9 + 9= 1800 + 40 + 18 = 1840 + 18 = 1858.
  • Now repeat it: double again to get 929 x 4 = 1858 + 1858 = 1800 + 1800 + 50 + 50 + 8 + 8 = 3600 + 100 + 16 = 3716
  • Finally, double again to get 929 x 8 = 3716 + 3716 = 3000 + 3000 + 700 + 700 + 10 + 10 + 6 + 6 = 6000 + 1400 + 20 + 12 = 7400 + 32 = 7432.

Trick # 6 – Multiplying by 5

This one is so super simple, and yet sometimes kids don’t know it and turn to a paper to work it out! To find 5 times any number, you first multiply that number with ten, then take half of that. Why is that easy? Because halving a multiple of ten is always easy!

Example 1:

  • Given – 38 x 5 = ?
  • First, multiply by 10:38 x 10 = 380
  • Then halve it! 380 ÷ 2 = 190.
    • If the halving is hard for you, find the nearest large number you would know easily. In this case, 400 ÷ 2 = 200. Now work it down. So 380 ÷ 2 = 190. 
    • Or work up from the nearest large number that’s easy for you. 300 ÷ 2 = 150, then 320 ÷ 2 = 160, 340 ÷ 2 = 170; 360 ÷ 2 = 180 and then 380 ÷ 2 = 190

Does this help? Let’s try a harder example then.

Example 2:

  • Given – 929 x 5= ?
  • First multiply by 10. 929 x 10 = 9290
  • Halve this. 9290 ÷ 2 = ?
    • Let’s break this down shall we, so it’s more manageable? 9290 ÷ 2 = 9000 ÷ 2 +200 ÷ 2 + 90 ÷ 2
    • 9000 ÷ 2 = 4500.
    • 200 ÷ 2 = 100 
    • 90 ÷ 2 = 45
    • Add them up: 4500 + 100 + 45 = 4,645.
    • Pretty self-explanatory right?

Trick # 7 – Multiplying by 9

This is a super-easy way to multiply any number by 9! Multiply the number by 10 and then subtract the entire number from it. Let’s try it!

Multiply by 9 – Example 1:

  • You’re given: 77 x 9.
  • Step 1: First we go 77 x  10 = 770.
  • Step 2: Now subtract 77 from the product  770 – 77 = 694

Multiply by 9 – Example 2:

  • You’re given: 129 x 9.
  • Step 1: First we go 129 x  10 = 1290.
  • Step 2: Now subtract 129 from the product  1290 – 129 = 1161

Trick # 8 – Multiplying by 11

This is like a real magic trick – doesn’t need any actual brain power to do.

When you multiply a 2-digit number by 11, take your original number and put a space between the digits.Then add both numbers and put that into the center. Sounds sketchy right? Let’s try it!

Multiply by 11 – Example 1:

  • You’re given: 25 x 11.
  • Step 1: First we go 2_5.
  • Step 2: Now we add 2 + 5 = 7 and
  • Step 3: Put that in the center  275
  • Step 4: Go ahead, check your answer! 25 x 11 = 275

But, wait a minute, what if the sum has 2 digits. Let’s try that!

Multiply by 11 – Example 2:

  • You’re given: 99 x 11.
  • Step 1:First we go 9_9.
  • Step 2: Now we add 9 + 9 = 18
  • Go ahead and put the 8 in the center, but make sure you carry the extra 1. So (9+1)89.
  • 99 X 11 = 1089
  • That easy, really!
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