How to multiply easily two 3-digit numbers in your head, for example 234 x 234:
200 x 200 = 40,000
200 x 30 = 6,000
200 x 4 = 800
30 x 200 = 6,000
30 x 30 = 900
30 x 4 = 120
4 x 200 = 800
4 x 30 = 120
4 x 4 = 16
40,000 + 6,000 + 800 + 6,000 + 900 + 120 + 800 + 120 + 16 = 54,756
