[wizzwizz4]

Multiplication and division by 2 and 5 correspond to each other. Multiplication by 11 is shift-and-add. There are many such tricks.

[Dylan16807]

The first one doesn't help with remembering times tables. The second one is outside the 1-10 times table we were talking about.

[wizzwizz4]

6 is 2×3, so 6×5 = 30. Likewise, 17 = 2×8 + 1, so 5×17 = 85.