Every die follows one rule: the front face and the back face always add up to 7.
If a die shows a 1, its back face is a 6 (because 1 + 6 = 7).
Flip both dice in the problem first, then do the math.
Example: 1 + 4 flips to 6 + 3, so 9.
This really pays off with minus - 2 − 5 does not work, but flipped it says 5 − 2 = 3.
Example
For parents
What does this exercise practice?
Flipped dice combines a die's spatial opposite-faces rule with a real calculation - the child has to convert both numbers first and must not compute the printed problem the way it looks.
Common pitfalls
The most common slip is calculating with the visible pips instead of the flipped ones. It helps to say the two numbers that are really meant out loud before each problem.
How to practice at home
Try it with two real dice - roll them, guess the back faces, then actually turn the dice over and check the answer.
Related: What's on the Bottom?, Calculating with Dice, Mirror numbers