The Magic Number 6
Sometime back Science Olympiad Foundation shared below post, image of which explained the magic of number six when doing multiplication. While they have already included additional information given by me for number > 10, this post explains it in details. The magic is - To multiply any number with 6, put that number in ones position, and number/2 in tens (or greater than tens) position. Basically, And this rule applies to both odd and even numbers. Let's start with simple examples with even number first: Example 1: 8 x 6 Here, N = 8, and N/2 = 4 8 x 6 = [N/2][N] = 48 For even numbers N >= 10: Example 2: 10 x 6 Here, N = 10 ( 1 is a forward carry) N/2 = 5 (+ carry) 10 x 6 = [N/2][N] = [5][10] = [5+1][0] = 60 Example 3: 28 x 6 Here, N = 28 ( 2 is a forward carry) N/2 = 14 (+ carry) 28 x 6 = [N/2][N] = [14][28] = [14+2][8] = 168 Example 4: 102 x 6 N = 102 ( 10 is a forward carry) N/2 = 51 (+ carry) 102 x 6 = [N/2][N] = [51][