Skip to content / Đến nội dung
ThichHocToan.com

2022 AMC 12B Question 22

AMC12 · 2022 AMC 12B

Question 22

Ant Amelia starts on the number line at $0$ and crawls in the following manner. For $n = 1,$ $2,$ $3,$ Amelia chooses a time duration $t_n$ and an increment $x_n$ independently and uniformly at random from the interval $(0, 1).$ During the $n$th step of the process, Amelia moves $x_n$ units in the positive direction, using up $t_n$ minutes. If the total elapsed time has exceeded $1$ minute during the $n$th step, she stops at the end of that step; otherwise, she continues with the next step, taking at most $3$ steps in all. What is the probability that Amelia’s position when she stops will be greater than $1?$
  1. $\dfrac13$
  2. $\dfrac12$
  3. $\dfrac23$
  4. $\dfrac34$
  5. $\dfrac56$