Marnie, this is a tricky one, but it deals with logic. There are 4 skiers, right? When the official times are posted, they are all compared to the winner, who doesn't have a time.
Let's take a race with three skiers. If Fred is 2 minutes and 3 seconds slower than John and Adam is 5 minutes and 4 seconds slower than John, then the results would be listed as such:
1. John Smilth
2. Fred Jones +2:03
3. Adam Williams +5:04
The plus is for a slower time, since you'd have to add 2 minutes and 3 seconds John's time to get Fred's time.
If we compare John's time to Adam, however, John's time is -5:04, because you have to subtract 5 minutes and 4 seconds from Adam's time to get John's time.
Let's go one step further and compare John and Adam's times to Fred. Then John's time is -2:03, but Adam's time becomes +2:59.
Remember that your question is saying that times are compared to yours! Hope this helps.