Viagogo OA题目以及详细解答过程

前几天海投了Viagogo，很快收到了OA，以下是OA的题目以及我的详细解答过程，求大米！
1. Probability

You go to a dinner party with 5 other guests, everyone is seated randomly around a round 6-person table. You know one other person at the party. Express below as a fraction in the simplest form (i.e. 1/2 instead of 2/4)
1. What is the probability you are sat next to the person you know?
2. What is the probability you are sat opposite the person you know?
3. What is the probability you sat next to two strangers?

解题思路：
total number of arrangement = 6!/6=120
1. 你的位置fix了，你朋友的位置fix了，剩下还有4个人随意排位（4!），同时考虑到你和朋友的位置可以调换，所以公式应该是：(4!*2)/120 = 2/5
2. 你的位置fix了，朋友必须坐在你对面，所以也fix了，剩下四人随意排位，所以公式为：4!/120=1/5
3. 1-第一小问的probability = 1-2/5 = 3/5

2. Logic
You have a biased coin that lands heads 10% of the time. You win $1000 every time the coin lands heads, and lose $50 every time

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000 into a bank account with 1.25% APR and left it. You now have $ 138,124.54. How many years have you left it in the bank for (to the nearest whole year)?

100,000 * (1+1.25%)^x = 138,124.54,解出x=26

看面经，求大米，看面经！