Multiplication: Rainbow Method

 Hello! Today I will teach you how to multiply quicker than you already can with a method known as the Rainbow Method. This is a shortcut on how to multiply any 2 digit number with any other two digit number.

Example: 23 x 55

Step 1: To calculate the first two digits of your answer, multiply the first digit of the first factor to the first digit of the second factor. Then leave a space after the answer.

23 x 55     Answer: 10_

Step 2: To calculate the last digit of your answer, multiply the last digit of the first factor to the last digit of the second factor. If its a two digit number, carry over the tens place digit to the space before.

                                                                                       1

23 x 55        Answer: 10_5

Step 3: Now, to calculate the final digit of the answer (the space) you will use the Rainbow Method. Simply multiply the first digit of the first factor to the last digit of the last factor, and add that to the product of the last digit of the first factor to the first digit of the last factor, as shown below:

                                              

This shows that you are adding "2 x 5"(as shown in the outer rainbow line on the picture) to "3 x 5"(as shown in the inner rainbow line on the picture). The sum is 25. This is what you put in the space in the answer. Since it is a 2 digit number, carry over the tens place digit of this number to the place before in the answer.

                                                                                      21

23 x 55          Answer: 1055 

Step 4: Now do your finishing touches on your answer by adding the digits you carried over to the digits below them, as shown below.

                                                                                                                   21

23 x 55          Answer: 1055 

                                                                        

                                                                          True Answer: 1265

The answer is therefore 1265. I hope you've learned how to use this method! If you have any questions, please post a comment below about it. Thanks!