Homeschool How To Kids Math

Math Tricks: How to Multiply By 11 Quickly

multiply by 11

Do you want to be popular at parties? Do you want your phone to be filled with texts, messages, and invitations? Well, have we got a way to make sure none of that happens! Just show them your amazing ability to …multiply by 11 in your head. Math tricks won’t make you popular, but they’ll make you smart.

It’s pretty simple. Really.

To multiply two numbers by 11, do the following:

Pick your number – say 23.

23 X 11

The first number – 2 – is your first number.

The second number – 3 – is your last number.

Now add the numbers together – 5. That’s your middle number.

So, 23 X 11 = 253.

42 X 11 = 462

35 x 11 – 385

Got it?

What if the numbers add up to more than 10? Well, just carry the one over to the first number.

64 X 11

Since  6 + 4 = 10, add “1” to the 6.  So, your first number is 7.

Middle number will be the “0” digit of the 10.

Last number will be the 4.

64 X 11 = 704

83 X 11 = 913

76 X 11 = 836

Understand that? Do it on paper first until you get the hang of it.

To multiply three numbers by 11, do the following:

Pick your number – say 231.

Your first number is your first number – 2.

The last number – 1 – is your last number.

Now add the first two numbers together – 5. That’s your second number.

Now add the last two numbers together – 4. That’s your third number.

231 X 11 = 2541

435 X 11 = 4785

626 X 11 = 6886

Making sense?

What if the numbers add up to more than 10? Well, just carry the one over like you did before.

372 X 11 = 4092

647 X 11 = 7117  (This one was tricky…you have to carry twice. Did you get it?)

Anyway, I’m sure your friends will be impressed. Maybe your in-laws will be proud of your new skill?

 

* Bonus Math Trick…to make sure everyone REALLY thinks you’re smart!

To easily square a number ending in 5 – like, 25, 35, 65, etc..do the following:

Let’s do 25.

Take the first number – the 2.

Now, take the 2 and add 1.

Multiply the 2 and 3.

2 X 3 = 6

Add “25” to the end.

625…that’s the answer.

So – 85 would be 8X9 = 72,  add the 25 to the end, and you get the answer of 7225.

75 would be 5625

45 would be 2025.

See…not that hard!

 

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