The next time your teacher wants you to compute a number, impress your classmates by doing the computations in your head- use mental math! There are several rules, tricks, and strategies to make what seems like complicated mathematical computations incredibly simple. We’ll cover many mental math tricks in future article posts, but let’s start off with a straightforward mental math rule you can begin using immediately.

There’s a simple rule for multiplying numbers by 11. Learn it quickly now and be on your way to mental math mastery.

When multiplying 11 times any two digit number, for example 45 x 11:

Add the two digit number together: 4+5= 9

Place the new number (9) in between the original two digit number 45: 495

Your final answer is then 495!

**Now you try the problem below..**

**35 x 11**

**Here's the answer..**

3+5= 8

Insert the 8 between the numbers in 35

Your final answer is 385.

**What about this problem?**

**49 x 11**

**Try it yourself then check the solution the solution. You should notice there is an additional step you will have to perform to get the correct answer.**

**49 x 11**

4 + 9 = 13

Insert the 13 between the numbers in 49

4(13)9

The additional step here is that you must carry over the 1 to the 4:

(4+1)39= 539 as your final answer.

(The additional rule here is that if after adding your two digit number you are left with a number larger than 9, you must carry the 1)

**Now try one more:**

**99 x 11**

**Here's the answer...**

9+9 = 18

Insert the 18 between the numbers in 99

9(18)9

Now carry over the 1 to the 9:

(9+1)89= 1089 as your final answer.

**When multiplying 11 times a three digit number, for example 426 x 11, the rules are a bit different.**

Add the first two digits of 426 together: 4+2= 6

Add the second two digits of 426 together: 2+6= 8

Next, drop the center number in your 426: 4__6 and insert the two numbers you calculated between what’s left: 4__6= 4686.

**Now try it yourself:**

**345 x 11**

**Here's the answer..**

3 x 4 = 7 and 4 x 5 = 9

Drop the 4 from 345: 3__5

Insert the two numbers you calculated: 3795

Your final answer is 3795.

At Action Potential Learning, we help train you to strengthen your natural mental abilities. Mental math is one way of improving your mental capabilities and keeping your mind sharp. Check back for future blog posts on new and interesting mental math tricks!

Article written by Shayna L. Pond and Action Potential Learning

Action Potential Learning provides private tutoring in math and science as well as standardized test prep. As math and science specialists, our tutors know and understand difficult math and science concepts and can help you improve your grades and perform on standardized tests.

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