15
12
6
10
Based on the provided information:
Since the distances XM and MY are equal for both trains (as they meet at the same point), the ratio of their travel times is inversely proportional to their speeds:
\[ \frac{t}{9} = \frac{10 - t}{t} \]
Upon cross-multiplication:
\[ t^2 = 9(10 - t) \] \[ t^2 = 90 - 9t \Rightarrow t^2 + 9t - 90 = 0 \]
Solving the quadratic equation:
\[ (t + 15)(t - 6) = 0 \Rightarrow t = -15 \text{ or } t = 6 \]
As time cannot be negative, the valid solution is:
\[ t = 6 \]
Train B's travel time:
\[ \text{From Y to M: } t = 6 \text{ minutes} \] \[ \text{From M to X: } 9 \text{ minutes} \] \[ \Rightarrow \text{Total travel time from Y to X = } 6 + 9 = \boxed{15} \text{ minutes} \]
Final Answer: 15 minutes
A box contains 16 red, 12 white, and 15 yellow identical marbles. A man picks one marble at a time without replacement. How many times must he pick a marble to be 100% certain of picking at least 3 white marbles?