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!
