Hello, frigidmars!
Did you make a sketch?
A train traveling at 30 mph reaches a tunnel which is 9 times as long as the train.
If the train takes 2 minutes to completely clear the tunnel, how long is the train? Code:
: - L - : - - - - -9L - - - - - : - L - :
*-------*-----------------------*-------*
| Train | Tunnel | Train |
*-------*-----------------------*-------*
A - - - - - - 10L - - - - - - - B
The length of the train is $\displaystyle L$ feet.
The length of the tunnel is $\displaystyle 9L$ feet.
. . The train is moving from left to right.
The train enters the tunnel with its front at $\displaystyle A.$
When the train is clear of the tunnel, its front is at $\displaystyle B.$
. . It has traveled $\displaystyle 10L$ feet.
Its speed is: .30 miles/hour = 2640 feet/minute.
Using: .$\displaystyle \frac{\text{Distance}}{\text{Speed}} \:=\:\text{Time}$, we have: .$\displaystyle \frac{10L}{2640} \:=\:2$
. . Hence: .$\displaystyle 10L \:=\:52380 \quad\Rightarrow\quad L \:=\:528$
Therefore, the train is 528 feet long.