# Cool Multiplication Math Trick Part 1

In this post, I am going to teach you another multiplication trick which you can use to calculate faster and share with your friends. This multiplication trick is quite similar to squaring a number ending in 5.

### The conditions to perform this trick are

(a) the sum of the ones digit is 10.

(b) the other digits (tens, hundreds, and so on) are the same.

Example 1: 23 × 27

This example fits the two conditions above. For (a), 3 + 7 = 10. Then, for (b) the tens digits are the same.

### The Math Trick

Step 1:  Add 1 to one of the tens digit, then multiply to the other tens digits.

In 23 × 27 That is (2 + 1) × 2 = 3 × 2 = 6.

Step 2: Multiply the ones digits.

3 × 7 = 21.

Step 3: Append the digits 621.

So, 23 × 27 =621.

Example 2: 62 × 68

Again, this example satisfies the two conditions above.  So,

Step 1: Add 1 to one of the tens digits and then multiply to the other tens digit.

(6 + 1) × 6 = 7 × 6 = 42

Step 2:  Multiply the one’s digits.

2 × 6= 16

Step 3: Append the digits: 4216.

So, 62 × 68 = 4216.

Example 3: 81  × 89

This satisfies conditions (a) and (b). So,

Step 1: Add 1 to one of the tens digits and then multiply to other tens digits.

(8 + 1) × 8 = 72

Step 2: Multiply the ones digits

× 9 =9

Step 3: Append the digits.

729?

Nope. This is where your estimation skills come in. As we can see,

80 × 80

is already equal to 6400, so there is no way that 81  × 89 = 729.

Actually, the correct answer is 7209.

In this multiplication trick, in case the one’s digits are 1 and 9, you must add 0 before the 0 in the product. Therefore, 51  × 59 = 3009, not 309

Example 4: 206 × 204

This multiplication also works for a higher number of digits such as in this example. In this example, we will treat the hundreds and tens digits as one number. So, step 1 will include multiplication of 20 by 21.

Step 1:  (20 + 1) × 20 = 21 × 20 = 420

Step 2: 6 × 4 = 24

Step 3: 42024

So, 206 × 204 = 42024.

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