Multiplication of Any Two-Digit Number with Any Two-Digit Number, Such that Their Ten's Digits are Equal, and Their One's Digits Add Up to Ten

In this Math Trick we are going to multiply any two-digit number with

any two digit number, Such that their ten's digits are equal, and

their one's digits add up to ten.

This is represented by the formula,

(10A+B) (10A 4C) = ;

A = (0,1...9), B+C = 10

Just multiply the ten's digit of the mulitiplicand plus one with the ten's

digit of the second number and write it down as the first and/or second digits or thousand's and/or hundred's digits of the answer,

and multiply the one's digits, and write it down as the third and fourth digits or ten's and one's digits of the answer.

We are going to solve three samples for this Math Tiick such as,

1. 29 x 21=

2. 37 x 33 =

3. 98 x 92 =

Let's proceed, 

1. 29 x 21= ;

(2 +1)2 = (3)2 = 6;

6 will be the first or hundreds digit.

For the 2nd and 3rd digits or tens and ones digits are 9 x 1 = 09.

The answer will be 609.

2. 37 x 33 = :

(3 + 1)3 = (4)3 = 12;

12 will be the first and second digits or thousands and hundreds digits.

For the 2nd and 3rd digits or tens and ones digits are 7 x 3 = 21.

The answer will be 1,221.

3. 98 x 92 = ;

(9 + 1)9 = (10)9 = 90;

90 will be the first and second digits or thousands and hundreds digits.

For the 2nd and 3rd digits or tens and ones digits are 8 x 2 = 17.

The answer will be 9,017.

You may notice that I made the multiplication from left to right. It actually has a purpose.You can immediately tell what's the first digit of the answer. And if it is a 3 or 4 digit number. 

This will be the beginning of solving it orally. You'll be amazed that you can solve it orally if you just continue practicing.