You have cited all the necessary rules for this. You put them together like this:
To do a group skill check, everyone in the group does the skill check. If at least half of the group succeeds, the entire group succeeds. Otherwise, the group fails …
Well, we need & # 39; half & # 39; of the group to succeed. What does "half" mean? In 5e we use normal language unless the book tells us to do something strange. In this case, as he quoted, the book make Tell us to do something weird instead! He says:
Whenever you divide a number in the game, round down if you end up with a fraction, even if the fraction is half or more.
So while half of 5 usually be 2.5, in this game it is 2. Similarly, when one applies these rules to the number & # 39; 3 & # 39; you can see that, because & # 39; 3 & # 39; It is an odd number, reducing it in half makes it end with a fraction. That means you round down and end up with the next whole number down, in this case & # 39; 1 & # 39 ;. Similarly, if you cut 1 by half, it would end with 0.
Keep in mind, however, that by doing this we are inventing what it means to "round down." In common language, you generally can't & # 39; round & # 39; without reference to something: & # 39; rounds to the nearest whole number & # 39; or & # 39; rounds to the nearest ten & # 39; or something like that. Used alone, the phrase is not clear: it could mean & # 39; to the nearest whole number & # 39; or & # 39; to the nearest integer & # 39; or & # 39; to the nearest non-fraction & # 39 ;, and not all of these are meanings that result in a reasonable game (although all, except & # 39; not fraction & # 39; because that is an incoherent idea in its expression usual, means 3/2 rounds to 1). Since rounding to the nearest whole number is the least terrible rule in general, when this rounding rule is used, it must be assumed that it does.