Multiply a repdigit number by a single digit number

Find a trick here that can help you multiply a repdigit number less than 100 by a single digit number in less than 2 seconds as long as you know your multiplication table.

What is a repdigit number? A repdigit number is a number whose digits are the same. For example, 55 and 77 repdigit numbers.

What is a single-digit number? A single-digit number is a number that has only 1 digit. For example, 4 and 8 are single-digit numbers.

The trick to follow is shown in the 3 examples below

Example #1

44×9 = ?

Step 1: Multiply 4 by 9 to get 36. Write 36 down with a space between 3 and 6

Step 2: Add 3 and 6 to get 9

Step 3: Put 9 between 3 and 6.

44×9 = 396

Example #2

88×5 = ?

Step 1: Multiply 8 by 5 to get 40. Write 40 down with a space between 4 and 0

Step 2: Add 4 and 0 to get 4

Step 3: Put 4 between 4 and 0.

88×5 = 440

Example #3

99×9 = ?

Step 1: Multiply 9 by 9 to get 81. Write 81 down with a space between 8 and 1

Step 2: Add 8 and 1 to get 9

Step 3: Put 9 between 8 and 1.

99×9 = 891