A Square and New Dice

Two simpler problems this week:
  1. In a 3x3 grid, place the numbers 1 to 8 in the outside squares such that on each side of the grid, the two corners sum to the number between them.
  2. One of my daughter's new games is called "Sum Swamp". It comes with two regular dice and a third (6-sided) "operation" die. The operation die has three "+" symbols and three "-" symbols. To determine the distance to move, all three dice are rolled. If a "+" appears, the numbers on the regular dice are added. If a "-" appears, the smaller (or equal) number is subtracted from the larger (or equal) number. What are the probabilities of each possible roll, and what is the average roll for these dice?

Source: Gabe, citing Hard to solve brain teasers. Original.

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