Master the 7 pillars of school success
Improve your grades and lower your stress
Learn to multiply any number by 11 rapidly. Using this Math trick you can multiply two digit numbers in your head faster than a calculator. The first trick will teach you how to multiply two digit numbers by 11, and the second trick will show you how to multiply three or more digit numbers by 11. This trick does not work for decimals.
Step 1. The first digit of the answer is the first digit being multiplied, which equals 4.
Step 2. The last digit of the answer will be the last number being multiplied,
which equals 3
Step 3. The middle term will be the sum of the two digits added together.
4 + 3 = 7
Final Answer =43 x 11 = 473
If the two terms added together for the middle term is greater then nine, then move a one to the left.
5 is the first term, 8 is the last, and add 5 + 8 = 13
13 is greater than 9 so move a 1 to the left.
Final answer = 638
To sum this trick up, add the digits and place the answer in between.
45 x 11 4+5 =9, place in between 4 and 5, final answer 495
78 X 11 = 7+8 =15 ( move a 1 to the left) final answer 858
62 x 11 = 6+2 in between 62 = 682
81 x 11 = 8+1 in between 81 = 891
Multiply by 11 Trick
Multiply 43 x11
Multiply 58 x 11
Multiply a three or greater digit number by 11
Example Problem: 3421 x 11
The first digit in the answer will be the first digit of the number being multiplied by 11
In this case it is 3
The last digit in the answer will be the last digit of the number being multiplied.
In this example it is 1
Now for the middle digits you start at far right and add pairs of numbers together
3421 x 11
3 4+3 =7 2+4 =6 1+2 =3 1 the final answer will be 37,631
The first digit of the number multiplied is 5 so the first digit of the answer is 5, and 2 is the last digit is 2.
Now to get the middle terms start at the right and add pairs of numbers as you move to the left.
2+3=5 then 3+4 =7 then 4+2 =6, and finally 2+5 = 7
Combine these for the answer 576,752
Solution
6 is the first digit 2 will be the last
Start adding right to left.
2+3 = 5 3+6 = 9 6 + 5 = 11 you can’t have a 2 digit number so move one to the left.
5+6 = 11 +1 from previous pair =12 then move one to the left.
As a result the first digit will equal 6 + 1 = 7
Final answer = 7 2 1 9 52
656,32 x 11
576,752 x 11
Advantages
- Fast,easy, and only involves addition
- Can multiply 11 in your head
Disadvantages
- Doesn't work with fractions
- Limited to 2 digit numbers