Perkalian dengan 2 : Menghitung Cepat

1 x 2 = 2 = 1 + 1
2 x 2 = 4 = 2 + 2
3 x 2 = 6 = 3 + 3
4 x 2 = 8 = 4 + 4

5 x 2 = 10 = 5 + 5
6 x 2 = 12 = 6 + 6 = (5 + 1) + (5 + 1) = 5 + 5 + 1 + 1 = 10 + 1 + 1 = 10 + 2 = 1|2 = 12
7 x 2 = 14 = 7 + 7 = (5 + 2) + (5 + 2) = 5 + 5 + 2 + 2 = 10 + 2 + 2 = 10 + 4 = 1|4 = 14
8 x 2 = 16 = 8 + 8 = (5 + 3) + (5 + 3) = 5 + 5 + 3 + 3 = 10 + 3 + 3 = 10 + 6 = 1|6 = 16
9 x 2 = 18 = 9 + 9 = (5 + 4) + (5 + 4) = 5 + 5 + 4 + 4 = 10 + 4 + 4 = 10 + 8 = 1|8 = 18

Rumus Umum :

1. XYZ x 2 = XYZ + XYZ
2. XYZ x 2 = X + X|Y + Y|Z + Z