【Key Point】Worst-case principle.
【Analysis】The first key is tried 10 times, the second key is tried 9 times......, the 10th key is tried 1 time; therefore, the maximum number of attempts is $10+9+8+7+6+5+4+3+2+1=55$ (times).

【Answer】 55
【3】A key can only open one lock. Now there are 10 different locks and 11 different keys. If you need to find the key for each lock, you would need to try $(\quad)$ times at most to correctly match each lock with its key.