A dice net that opposite sides add up to 7?

Answer 1

There is no actual 'necessity' for the opposite sides to add to seven. As long as the numbers are all present, the die would still be fair and proper, and the probability of rolling any particular number would be constant - 1/6. Custom and practice is the only reason that the numbers are arranged so that they add to seven. I suppose it prevents arguments - if a player was loosing at a dice game they might be tempted to claim that the dice are non-standard if they were different from other dice.

Answer 2

I'm not sure I understand your question. But a dice with opposite sides adding up to 7 is just a regular dice. E.g. 1 and 6 are opposite. 2 and 5, 3 and 4. All of these add up to 7.